Heat oven to 180C/160C fan/gas 4. Grease a 20 x 30cm baking or roasting tin and line with baking parchment. To make the sponge batter, beat the butter, flour, sugar, baking powder, eggs, yogurt, vanilla, cocoa and half the coffee in a large bowl with an electric whisk until lump-free. Spoon into the tin, then bake for 25-30 mins until golden and risen and a skewer poked in comes out clean. Drizzle with some of the remaining coffee.