• Preheat conventional oven to 350°F / 180°C. Line 2 - 9 x 9 inch metal square pans with parchment paper using butter. Leave an overhang of parchment paper on 2 opposite sides. Or you can use 1 - 9 x 13 inch metal pan as well.

Chocolate chip cookie layer

Making brown butter

• Place the butter in a stainless steel pan or saucepan, and heat over medium heat to melt. When the butter has melted, add the milk powder and whisk it in to dissolve in the butter.
  226 g unsalted butter, 2 tbsp milk powder
• Using a whisk or spatula, frequently mix the butter to prevent the milk solids from catching at the bottom of the pan and burning.
• The butter will start to boil. Continue to heat the butter while whisking frequently. The milk solids will separate and sink to the bottom of the pan. Continue to heat and whisk, and the milk solids will start to turn light golden in color. Keep heating the butter and frequently mix it with the whisk.
• As the butter cooks, the milk solids will continue to darken in color and turn a toasty dark golden color. Immediately remove the pan from the stove and pour the butter into a heat-proof bowl. Let it cool slightly.
• When the butter has cooled down slightly, add the whiskey or water to the butter. Add this liquid slowly, since the butter will bubble up if it's too hot when you add the liquid.
  30 - 45 mL tbsp whiskey

Making the brown butter chocolate chip cookie layer

• Place the warm brown butter, sugar, and salt in a large bowl. Using a hand-held electric mixer, mix the butter and sugar well.
  350 g dark brown sugar, ½ tsp salt
• Add the vanilla and the eggs, and whisk them in until smooth. Continue to mix the batter for about 3 -4 minutes on medium speed, until the batter becomes a shade lighter in color and is slightly thickened. The hotter the batter, the longer this might take, but if the batter is too cold, it won’t mix well.
  2 tsp vanilla extract, 2 large eggs
• Add the flour and fold it in, in 2 - 3 additions. Be careful not to overmix the batter.
  280 g AP flour
• Add the chopped chocolate with the last addition of flour, and fold it in.
  80 g chopped chocolate chunks
• Set the batter aside.

Chocolate brownie layer

• Place the butter, chocolate, both types of sugar, and salt in a large bowl. Heat in 30 second increments in a microwave while stirring in between to almost melt all the butter and chocolate together. This can take about 30 - 90 seconds, depending on the microwave.
  226 g unsalted butter, 150 g brown sugar, 150 g white sugar, ½ tsp salt, 115 g dark chocolate
• Stir to dissolve the remaining butter and chocolate in the residual heat.
• Dissolve the coffee in the vanilla, and add this to the melted chocolate-butter mixture.
  2 tsp vanilla extract, 1 tsp coffee extract
• Add the eggs and whisk them in.
  3 large eggs
• Using a hand mixer, whisk the butter-sugar-egg mix on medium high speed, until the batter becomes a paler color (3 – 4 minutes) and is thick.
• In a separate bowl, sift the flour and cocoa powder together.
  56 g cocoa powder, 90 g AP flour
• Add the flour-cocoa mix into the wet ingredients (in two batches if that's easier) and mix it in until just combined. Do not overmix the batter. Set aside.

Making the brookies

Swirled brookies

• Using an ice cream scoop, alternate the addition of brownie and cookie dough batter into each of the pans. Make sure that each pan gets an equal amount of the brownie and the cookie batter.
• Gently drag a butter knife or small palette knife through the batter to create fairly large swirls (so that the batter doesn’t mix too much and stays separate).

  If you'd like to layer the two batters instead, follow the instructions below.

Layered brookies

• Divide the brownie batter in half (either by weight or with a scoop) and add it to each of the pans.
• Then divide the chocolate chip cookie batter in half. Dollop the cookie layer over the brownie layer. If the dough is stiff (it will thicken more as it cools down), you can flatten it with your hands before placing it on the brownie layer. The whole surface need not be totally covered - it's OK for the brownie batter to peek through in some places.
• OPTIONAL - Sprinkle some maldon sea salt flakes and chopped chocolate on top.
  50 g chopped dark chocolate, Maldon sea salt flakes

Baking

• Place the baking pans in the preheated oven and bake for about 35 - 40 minutes.
• If you insert a clean toothpick into the center of the pan, it should come out with a few crumbs attached to it, and no raw batter.
• Remove the pans from the oven and let the brookies cool down. When it’s almost cooled down, gently lift the parchment paper to loosen the brookies from the pan, but not to lift them out of the pan. Let the bars completely cool down in the pan.
• Once cooled, remove the bars from the pan using the parchment paper and a spatula.
• Cut each brookie pan into 4 x 4 pieces, for a total of 16 pieces per pan (32 pieces total). To get nice clean slices, use a straight blade warm knife and wipe the blade clean between each cut.