Chocolate and Butter Mixture
Cut 100g of chocolate and 60g of butter into small pieces. Place them in a heatproof bowl.
Melt them using a double boiler, stirring continuously until smooth. Set aside to cool slightly.
Brownie Batter
In a clean bowl, crack 2 eggs and add 30g of granulated sugar. Pour in 15ml of milk. Mix with a whisk until the mixture lightens in color and the milk is well combined.
Sift 30g of cake flour and 5g of cocoa powder into the egg mixture. Mix with a whisk until no dry flour remains and the batter is smooth.
Pour the cooled chocolate-butter mixture into the batter. Stir until fully combined.
Baking the Brownie
Preheat the oven to 160°C (320°F) in top and bottom heating mode.
Line a 6-inch square pan with parchment paper for easy removal. Pour the brownie batter into the pan and smooth the surface with a spatula.
Place the pan on the middle rack of the preheated oven and bake at 160°C for 25 minutes.
Check doneness by inserting a toothpick. If it comes out with moist crumbs (but not liquid batter), it is done. If the toothpick has more batter, bake for a few extra minutes but avoid overbaking.
Once baked, let the brownie cool on a wire rack.