Preheat oven to 325°F. Line a quarter pan sheet with parchment paper and butter the sides generously.
Place the butter, sugar, salt, vanilla and cocoa powder in a bowl and mix to form a smooth paste.
Add the egg whites and whisk in, until completely incorporated and smooth.
Sift the AP flour and baking soda into the mix, and fold the flour in to mix well.
Scrape the batter into the prepared pan and spread it out evenly using an offset spatula.
Bake in preheated oven for exactly 15 minutes.
Remove from the oven and let it cool down completely.
Butter Toffee Layer
Place the butter, sugar, vanilla and salt in a high edged saucepan (since this mix will bubble up while cooking).
Heat over medium heat, mixing occasionally to melt the sugar completely and to bring the mix to a boil.
Place a sugar thermometer in the saucepan and heat the sugar mix until it reaches 305°F (between 300-310°F). Stir occasionally to distribute the heat. The sugar will turn a golden amber color when it's ready.
While the sugar is cooking, roughly chop the chocolate wavy lays potato chips to pieces (do not crush them).
When the toffee is ready, pour the toffee layer over the cooled down brownie layer, and spread it while it’s still hot.
Sprinkle the chocolate chips, chocolate wavy lays potato chips, chopped pretzels and salt over the hot toffee. Press down the wavy lays chips and pretzels into the caramel to make sure they are embedded.
Leave to cool for 1 - 2 minutes. The chocolate chips will have softened at this stage and can be spread on top (around the chips and pretzels).
Let it sit for at least 2 hours to let it completely set.
Remove the brittle from the pan and break it into pieces. Store in an airtight container.
Recipe from The Flavor Bender by Dini Kodippili
Sweet and Salty Brownie And Butter Toffee Brittle https://www.theflavorbender.com/sweet-salty-brownie-and-butter-toffee-brittle/