1. In a small saucepan, place the butter and add the chopped chocolate. Heat gently until melted, then stir in the carob powder. In the mixer bowl, add the eggs and sugar and beat until they become fluffy and creamy.
2. Using a spatula, gently fold the melted butter and carob mixture into the eggs using circular motions. Pour the batter into a 20cm square baking pan lined with non-stick parchment paper.
3. Spread the batter evenly and sprinkle the walnuts on top. Bake in a preheated oven at 180°C for 25-30 minutes, until the center of the brownie is still soft and the edges are crisp.