Chop ⅓ cups (50 grams) chocolate into small pieces and place in a bowl. Stand aside
In a saucepan, heat the butter and the remaining chocolate over low heat until the chocolate has melted. Stir and allow to cool.
In a second bowl put the eggs, sugar, vanilla extract, baking powder and salt.
Blend for 5 minutes until everything is fluffy.
Using a spatula, mix the flour and cocoa powder into the batter.
Take the small pieces of chocolate (from step 1) and mix them through the batter with the spatula.
Spoon the walnuts into the batter.
Cover the bowl with plastic wrap and refrigerate for at least 30 minutes.
Meanwhile, preheat the oven to 180 degrees Celsius.
Line a baking tray with parchment paper.
Take a small ice cream scoop (or 2 tablespoons) and scoop small balls of batter on the baking sheet. Keep sufficient distance (about 3 cm) between the cookies, because they will run slightly during baking.
Bake the cookies for 10 minutes.
Remove the Brookies from the oven and let them cool for 5 minutes. Then carefully remove them from the baking tray with a spatula and place them on a wire rack.