Preheat the oven to 350 degrees F, 175C. Line a 8x12 inch or similar pan with parchment paper.
In a saucepan melt the butter on medium heat. The butter starts to get foamy with cracking and popping noises when the liquid evaporates. Once the crackling stops, swirl the pan until the butter develops a nutty aroma and brown bits start to form at the bottom. Once the bits are amber in color remove the pan from heat and add in the slightly chopped chocolate and stir until melted.
Combine the eggs and sugar.With a hand mixer or a stand mixer beat on medium-high speed until completely fluffy in texture and pale in color. This takes about 8-10 minutes. Add in the vanilla extract.
Mix the dry ingredients together and add in the eggwhip with a sieve.
Mix at a low speed for some seconds and pour in the butter and chocolate mix. Mix gently and add in as last the nuts.
Pour the batter in your pan and even it out with a spatula. Bake for 25 minutes. Let the brownies cool down before serving.
Notes
The brownied store in the fridge for 7 days and at room temperature for 2 days.