Preheat oven to 180 degrees C or gas mark 4. Line a 20 x 30 cm cake tin with greaseproof paper.
Melt the butter, sugar & cocoa powder in a pan over a gentle heat. Leave to cool then beat in the flour, nuts and eggs (beaten). Pour the mixture into the cake tin and bake for 25 minutes. DO NOT OVERCOOK! The brownies should have a fudgy texture.
You can halve the quantities but you might need to reduce the cooking time slightly unless you use a smaller tin!