Chocolate sheet cake

This American-style traybake is easy to make, can be prepared in advance, and cuts into even portions. Decorate it however you like: top with your choice of sweets and nuts, scatter over chocolate shavings and colourful sprinkles, or spell out a word using chocolate buttons. Serves 10 Prep 15 mins plus cooling and setting undecorated Cook 30 mins

185ml vegetable oil, plus extra

for the tin

250g plain flour

80g cocoa powder

2½ tsp baking powder

1 tsp bicarbonate of soda

325g light brown soft sugar

250ml buttermilk

125ml strong coffee or espresso, cooled

until just warm (not hot)

2 tsp vanilla extract

2 large eggs

FOR THE ICING

150g salted butter, softened

200g icing sugar

4 tbsp cocoa powder

2 tbsp milk sweets, sprinkles, chocolate shavings

or nuts, to decorate

1 Heat the oven to 180C/160C fan/gas 4. Oil the base and sides of a 33 x 23cm roasting or cake tin (it should have a rim of at least 2½cm) and line with baking parchment. Combine the flour, cocoa powder, baking powder, bicarb, sugar and a large pinch of salt in a large bowl. Rub any lumps of sugar between your fingers to break them up, shaking the bowl a few times to bring them to the surface.

2 Whisk the oil, buttermilk, coffee, vanilla and eggs together in a jug, then pour the mixture into the dry ingredients. Stir well using a spatula, ensuring you mix in any pockets of flour. Pour the batter into the prepared tin and bake for 25-30 mins, or until a skewer inserted into the middle comes out clean. If any wet mixture clings to the skewer, bake for 5 mins more, then check again. Once cooked, remove from the oven and leave to cool in the tin for at least 20 mins. Once completely cool, the cake can be frozen for up to three months.

3 Meanwhile, make the icing. Melt the butter in a saucepan, then remove from the heat and stir in the icing sugar, cocoa powder and milk. The icing will be very runny, but will thicken a little as it cools

(if the icing has set too much before the cake has cooled, reheat it slightly to make it easier to pour).

4 Pour the icing over the cake and leave to set. Decorate with sweets, sprinkles, chocolate shavings or nuts, then cut into squares and serve.

PER SERVING 330 kcals, fat 18g, saturates 6g,

carbs 37g, sugars 26g, fibre 2g, protein 4g, salt 0.5g