Preheat oven to 180. Grease and line a 23 cm square tin. Melt 250g butter with 325g sugar, remove from heat. Sift 90g cocoa, 4 Tbsp flour, pinch salt and half tsp baking powder. Stir in melted butter and sugar, add 4 eggs and mix. Add 125g chopped nuts (I use pecan), I sometimes replace nuts with frozen cranberries (as in picture below), and 200g chopped dark chocolate, mix to combine. Pour into prepared tin and bake for about 25 minutes.