Pre-heat the oven to 170 C
In a bowl, mix 1 and 1/3 cups of sifted plain flour, 2 and 1/4 cups of sugar, 1 cup of cocoa powder, and 1/4 teaspoon of baking powder. Place the dry ingredients in a food processor and add 4 eggs and 250grams of melted butter (it's probably best to cool it so you don't scramble the eggs!) Process till smooth.
Pour the mix into a lined 20cm cake tin and bake for about 40 minutes.
I could suggest that you make them for friends and family as Christmas gifts, but instead I'm going to suggest you make a pan for yourself, brew yourself a pot of strong coffee, put your feet up and enjoy!