Preheat the oven to 180°C, gas mark 4. Base line a 22cm square tin.
Whisk the eggs and sugar together until pale and creamy. Sieve the flour and cocoa together and gently whisk into the eggs, then whisk in the oil.
Pour into the prepared tin, scatter over the cranberries and chocolate chips if using. Bake for 25-30 minutes. Cool slightly before turning out of the tin. Cut into 12 pieces.
Replace the cranberries with any other dried fruit such as apple or chopped dates. For an extra healthy option, replace the flour with self-raising wholemeal flour.