Preheat oven to 180°C (160°C fan)
Grease and line a 9x9 baking tin
Put all the ingredients (except the chocolate chips) into one large bowl
Mix with an electric whisk or stand mixer for about 2 minutes until smooth and creamy
Stir in the chocolate chips
Pour into your baking tin and spread evenly
Bake for 25–30 minutes, until a skewer comes out clean
Leave to cool before adding your chocolate topping