Start by placing 1 cup (230 g) of unsalted room temperature butter in a light colored pan, keep it on medium-low heat, and stir constantly. First, it will melt, then it will start to bubble. Once bubbles appear, it will shortly start to brown. The color will be a deep golden brown or amber. Let the butter cool slightly for 5 minutes before you use it.
In a mixing bowl, combine slightly over 1/3 cup (80 g) granulatedsugar, 2/3 cup (140 g) brownsugar, and 1 tsp (6 g) salt, 1 ½ tsp (7 g) vanillapaste. Whisk until all is combined. Add the cooled brown butter and mix. Add 2 room-temperature eggs and 1 tsp (4 g) bakingpowder, whisk.
Add 2 ½ cups (320 g) all–purposeflour and, using a spatula, combine it. When the cookie dough is not warm, add ½ cup + 2 tbsp (100 g) darkchocolatechips or callets.
Line an 8-inch (20 cm) square pan with parchment paper. Add most of the cookie dough on the bottom, removing 4 tbsp that you will use to top the brookies.
To prepare the brownies, start by adding 4 eggs with 2/3 cup (140 g) brown sugar and 3 ½ tbsp (40 g) granulatedsugar in a stand mixer bowl fitted with a whisk attachment. For the first 3 minutes, have the mixer at low speed. Then, increase to high speed and beat the eggs for 10 minutes
In a light colored pan, add 1 cup + 1 tbsp (240 g) room temperature unsalted butter. We will brown it again. Start by melting it on medium-low heat. After melting, it starts to bubble. When the bubbles increase, and you notice a nutty aroma and the butter has turned an amber color, it’s ready. To the hot butter, you want to add 1 ¾ cups (300 g) dark chocolate callets. Stir until it’s fully melted. Preheat the oven to 355 F (180 F)
In a mixing bowl, mix ¾ tsp (4.5 g) salt, 1 tsp (5 g) pure vanilla paste, slightly under ¾ cup (90 g) all-purposeflour, and 1 cup + 2 tbsp (90 g) cocoa powder. To this mixture, add the melted chocolate with butter. Once it’s all incorporated, fold in the beaten eggs.
Pour this brownie batter over the cookie dough layer. Add the 4 tbsp of cookie dough we set aside earlier randomly over this layer. Bake the brookies in the preheated oven for 1 hour.
After baking, let them cool in the pan for at least 45 minutes.