Butter the base and sides of two 20cm round sandwich tins and line the bases with baking parchment. STEP 2. In a large bowl, beat together 200g golden caster sugar, 200g softened unsalted butter, 4 large eggs, 200g self-raising flour, 2 tbsp cocoa powder, 1 tsp baking powder, ½ tsp vanilla extract, 2.