175g unsalted butter, chopped, plus extra to grease
150g dark chocolate (70% cocoa solids), chopped
3 medium eggs
300g caster sugar
75g plain flour
40g cocoa powder
Icing sugar, optional, to dust
1. Melt the butter and chocolate together in a heatproof bowl set over a pan of barely simmering water (make sure the base of the bowl doesn't touch the water)
When the mixtre is melted and smooth, lift the bowl off the pan and set aside to cool for 20min.
2. Preheat oven to 180ºC (160ºC fan) mark 4 and lighly grease and line a 20.5cm square tin with baking parchment. Using a handheld electric whisk, beat the ggs and ugar together in a large bowl until thick and moussey - about 5 min .
3. Add the melted and cooled cocolate mixture to the egg bowl and fols together with a large metal spoon. Sift over the flour, cocoa powder and a pinch of salt and fold together
4. Scrape the mixture into the prepared tin, level and bake for 30min or until there is no wobble left when you gently shake the tin. Cool completely in the tin before dusting with icing sugar (if you like) and cutting into squares