Instructions

Preheat the oven to 180C/160Fan/Gas mark 4. Butter and line a 9x13inch (with a 2 inch depth) traybake tin with baking parchment.
Using a free standing electric mixer, hand whisk or a wooden spoon and large bowl, beat the butter and sugar together until very light and fluffy, at least 5 minutes. Using a rubber spatula, scrape down the mixture that’s sticking to the sides of the bowl.
Beat in the eggs, one at a time, making sure each one is well incorporated before adding the next. Stir in the vanilla extract. Using a large metal spoon, lightly fold in the flour, taking care not to overbeat the mixture.
Spoon the mixture into the prepared tin, smooth the top and bake for 40-45 minutes or until the cake is springy to touch and golden. A skewer inserted in the middle of the cake should emerge clean. Transfer the cake to a wire rack and leave to cool completely in the tin.
Mix the sieved icing sugar with enough water to make a thick but pourable icing glaze. Pour over the cold cake (I leave the cake in the tin – it’s much easier) and decorate with sprinkles. Leave to set before cutting into squares and serving.