Rhubarb crumble bars that are super easy to make and a perfectly sweet, delicious summer treat! A tart, rhubarb filling sandwiched between a buttery shortbread base and a nutty crumble topping.
These delicious rhubarb bars with a crumble topping are vibrant in color and flavor, and taste like summer! And ridiculously easy to make too.
I love making the most of rhubarb during the very short rhubarb season in Canada.
These rhubarb crumble bars have been making an appearance in my kitchen repeatedly over the last month, and summer has only just officially begun! But the great thing is that you can easily adapt these dessert bars into strawberry rhubarb bars with a crumble topping, to make use of all the gorgeous strawberries available in summer as well.
These rhubarb bars start with a homemade rhubarb filling that is similar to a jam. I add some apple to the filling, purely to help thicken the filling properly to a jam-like consistency WITHOUT adding too much sugar.
This jam is then spread between a butter shortbread layer and a crumb topping that is made with the SAME dough! So you end up with a delightfully buttery, tart rhubarb bar that has just the right amount of sweetness!
Why I love this recipe
- The rhubarb jam filling is easy to make and can also be made in advance.
- The addition of apple in the filling makes it jammy WITHOUT having to add too much sugar.
- Can easily adapt this recipe to make strawberry rhubarb bars by adding strawberries to the rhubarb filling.
- You only need to make ONE dough, because the same shortbread dough is used for the base AND the topping.
- The dough requires no chilling, so it’s easy and quick to make and assemble.
- Add nuts or oats to the topping to make it more interesting!
- You can even use premade rhubarb jam to make this recipe, but I do prefer the flavor of this homemade rhubarb jam filling!
So let’s start baking.
Fresh rhubarb is obviously the most important ingredient for rhubarb bars! I have made this recipe with beautifully red rhubarb stalks as well as green stalks, and ones in between as well. When choosing your fresh rhubarb for this recipe, don’t worry about the color of rhubarb or the quality of the rhubarb. Some blemishes are absolutely fine as they can be removed prior to cooking.
The red rhubarb stalks will obviously produce a prettier color, but there won’t be a difference in taste. If you like though, you can substitute some of the rhubarb with some strawberries for flavor and color.
You CAN leave this out if you like. But I LOVE the additional tart flavor and jammy texture that apples add to the filling.
I use white sugar so that the flavor of rhubarb can shine through. I prefer not to use brown sugar for this recipe.
The fruity acidity from lemon juice will brighten up the filling flavor for a more summery rhubarb bar!
Shortbread base and topping
I use unsalted butter, so that I can control the salt level in my shortbread base. You can use salted butter, but be mindful to reduce the amount of salt you add to the recipe. There is no need to use frozen butter or cold butter in this recipe, as we will be using softened butter instead.
I add an egg to this recipe to act as a binder. As a result, the shortbread base isn’t too crumbly and will hold together very well.
I use caster sugar (white), so that the sugar will dissolve more readily in the dough, but you can use granulated sugar as well.
All purpose flour is ideal for this rhubarb recipe. You can use cake flour if you like and if that’s all you have. But avoid using bread flour, since the high gluten content in bread flour can make the shortbread tough.
Vanilla and salt are the only flavoring that I add to the shortbread base. You could also add a little almond extract if you like. Personally, I do not like almond extract however.
Optional topping ideas
The shortbread dough for the topping can be mixed with chopped nuts or other additions to make the crumble topping for your rhubarb crumble bars more interesting. This is optional though. Here are some ideas,
- Almond slices
- Coconut (desiccated or flakes)
- Cashew nuts
- Puffed quinoa
How to make the rhubarb crumble bars
Making the rhubarb jam filling
The first step is to make the jam. You can make this a few hours ahead of time, or even a few weeks ahead of time! If you make the jam more than 5 days ahead of time, make sure to freeze the jam until needed, and thaw it out before you use it.
Wash and dry the fresh rhubarb and cut them into 1 inch pieces.
Place the rhubarb in a large pot, along with the sugar, grated apple, lemon juice and water. Cook over medium heat while stirring.
The mixture will come to a boil and then thicken into a jam-like, thick consistency, almost like apple butter. The total cook time for me is between 35 – 40 minutes on low heat.
Place the rhubarb filling in a bowl or container and let it cool until it’s at room temperature. You can use it if it’s just a little warm, but not too warm, as it will melt the butter in the shortbread layer. You can also chill the jam for up to 5 days before you use it.
Shortbread base and topping
All the ingredients for this dough should be at room temperature, and the butter should be very soft. You can use a hand mixer for this if that’s convenient, but I just use my hands or a rubber spatula. If the butter is very soft, using my hands or a spatula is even easier. In winter, I may microwave the butter to soften it, but make sure it doesn’t melt.
In a large bowl combine the dry ingredients first. Then add the wet ingredients into the same large bowl. Mix well using a spatula or even your hands. I use my hands because it’s faster and easier. You should end up with a soft ball of dough. Make sure NOT to overhandle the dough because it will make the dough too tough.
You should end up with a dough that looks like this.
Separate the dough into two uneven portions – about ¾ and ¼. The ¾ portion will be used as the base, and the ¼ portion will be used for the topping.
Assembling the rhubarb crumble bars
Preheat the oven to 350 F / 180 C. While the oven is heating, prepare your 9 x 9 inch square pan for baking. You can either butter and flour the pan, or line the pan with parchment paper.
Take the ¾ portion of dough and press it evenly into the baking dish. Use a flat surface to help press and level the layer.
Next, take about 1 cup (it’s OK if it’s slightly more!) of the rhubarb jam filling and spread it evenly over the shortbread base.
Take smaller pieces of the leftover dough and flatten slightly. Place these slightly flattened pieces of dough on top of the jam layer to create the crumble topping. You can choose to put as much as you like to cover the jam in a thin layer of the shortbread dough, OR leave some gaps for the jam to peek through (like I did here in these pictures).
Bake the rhubarb crumb bars in the preheated oven for about 35 – 40 minutes. The top layers should be lightly browned when the bars are ready.
Remove the pan from the oven after baking and let it cool to room temperature, OR you can place it in the fridge overnight to chill the bars. They are definitely easier to cut when a little cold, but I won’t blame you for not wanting to wait until the rhubarb jam bars are chilled and ready! 🙂
To make strawberry rhubarb bars – You can replace 50% of the rhubarb with strawberries to make the filling. If you’re using ready-made jam, use ½ rhubarb jam and ½ strawberry jam.
To make strawberry crumble bars – Replace the rhubarb topping with this homemade strawberry jam instead.
Vegan options – Replace the butter with a vegan butter (not margarine) and instead of the egg, use about ¼ cup of plant-based milk to bring the dough together.
Can I make these rhubarb bars ahead of time?
Yes! The jam can be made weeks in advance, but you have to freeze the rhubarb jam until you need it. Then just thaw it before you spread it on top of the shortbread layer.
The dough can also be made ahead of time, but it’s so easy and quick to assemble, that I never really bother making it ahead of time. But if you like, here is how you can store the dough if you don’t want to make the bars right away.
Make the dough and flatten it into a disc. Wrap and store in the fridge for up to 2 days. When you’re ready to use it, let it soften slightly, and then remove about ¼ if the dough and set that aside for the topping. Then proceed with the recipe instructions for assembly.
My preference however is to make the rhubarb bars, bake them, and then store those for later instead!
Once the bars have cooled down, cut them into squares or bars (however you like). I usually cut them into 4 x 4 pieces (16 squares). Make sure to use a sharp knife to get those clean edges. Store the bars in an air-tight container.
Room temperature – about 2 days
Fridge – about 1 week
Freezer – about 2 months. If you’re storing them in the freezer, make sure to separate stacked bars with parchment paper to prevent them from sticking to each other. I also highly recommend that you wrap them in foil before storing it in an air-tight container. I find that this practice reduces the buttery shortbread from absorbing other smells from the freezer.
Some tips to get perfect rhubarb bars
You don’t HAVE to make the rhubarb topping in advance! Once you make the topping, spread it out on a quarter sheet pan and place it in the freezer or fridge to cool it down faster.
You can use red OR green rhubarb. It’s also a great recipe to use up rhubarb that’s a little bruised or wilted. You can also use frozen rhubarb to make the filling, if fresh rhubarb isn’t available.
Make sure to use a kitchen scale for the ingredients (especially for the shortbread dough). Adding too much flour can result in a dry and crumbly shortbread crust.
Easy Rhubarb Crumble Bars
- 450 g rhubarb cut into 1 inch pieces
- 150 g white sugar
- 65 g green apple, grated about 1 medium apple
- 1.5 tbsp lemon juice
- 4 tbsp water
- Pinch sea salt
Shortbread dough (base and topping)
- 300 g AP flour (spooned and leveled for cup measurements)
- 150 g white sugar
- ¼ tsp sea salt
- 226 g butter 2 sticks
- 1 large egg
- 1 tsp vanilla extract
- 3 tbsp sliced almonds or rolled oats optional
Rhubarb filling (makes about 1½ cups)
- Place the rhubarb, sugar, apple, lemon juice, water, and salt in a saucepan (I use a 5 qt / 1 L pot for 1 batch). Mix well to combine.450 g rhubarb, 150 g white sugar, 65 g green apple, grated, 1.5 tbsp lemon juice, 4 tbsp water, Pinch sea salt
- Place the pot over medium-high heat and cook until the mix comes to a boil. Stir frequently while cooking. This should take about 10 minutes.
- Reduce the heat to medium / medium-low and continue to cook the mixture while stirring frequently. The mixture may start to bubble, so be careful!
- Cook until the mixture starts to thicken and it looks like apple butter. This can take a further 20 – 30 minutes.
- Once thickened, remove from the heat and transfer the filling into a bowl. Let it cool down to room temperature. Cover and let it chill in the fridge until the next day if needed, but the filling can be used at room temperature (or slightly warmer as well).
- Make sure the butter is soft and at room temperature. You can use cold butter as well, but it will be harder to mix. If the butter is hard and not easily pressed, place the butter in a warm area until it’s soft (or microwave on low power). Do not let it melt.226 g butter
- In a large bowl, mix the flour, sugar and salt.300 g AP flour, 150 g white sugar, ¼ tsp sea salt
- Add the butter, egg, and vanilla.226 g butter, 1 large egg, 1 tsp vanilla extract
- Using a spatula, mix the butter, egg and flour mix together. You can also use your hands to mix the dough.
- Make sure the butter and egg are mixed through the flour uniformly and forms a soft dough.
- Divide the dough into two pieces – ¾ of the dough and a smaller ¼ of the dough. Cover the dough and let it rest while you prepare the baking pan.
Assembly and baking
- Preheat the oven to 350°F / 180°C.
- Butter and line a 9 inch square pan with parchment paper.
- Take the larger portion of shortbread dough (¾ portion), and press it into the bottom of the baking pan. Make sure the dough is pressed into a flat, even layer. Use a flat surface like a spatula or the bottom of a glass to evenly press the dough into the base.
- Spread about 1 cup of the cooled rhubarb filling over the shortbread layer.
- OPTIONAL – add the almond or oats to the ¼ portion of the dough. Break up the dough into smaller pieces and mix it with the nuts / oats.3 tbsp sliced almonds or rolled oats
- Take smaller pieces of the dough and flatten them slightly. Place these flattened dough pieces on top of the rhubarb filling layer. You can place enough to cover the whole rhubarb filling or leave some gaps to have the filling peaking through.
- Transfer the baking pan into the preheated oven and bake for about 40 minutes, rotating the pan once halfway through the baking time. Remove the pan from the oven when there is some browning on the surface.
- Let the bars cool down to room temperature. Preferably let it chill for a few hours in the fridge to make it easier to cut them into bars.
- Remove the rhubarb bars from the pan and cut into squares or bars. I cut them into 16 squares.
- Store the bars in an airtight container for up to 1 week in the fridge.
Tips & Tricks
Storage instructionsRoom temperature – about 2 days Fridge – about 1 week Freezer – about 2 months. If you’re storing them in the freezer, make sure to separate stacked bars with parchment paper to prevent them from sticking to each other. I also highly recommend that you wrap them in foil before storing in an air-tight container. I find that this practice reduces the buttery shortbread from absorbing other smells in the freezer.
“This website provides approximate nutrition information for convenience and as a courtesy only. Nutrition data is gathered primarily from the USDA Food Composition Database, whenever available, or otherwise other online calculators.”