Heat the oven to 180C/160C fan/ gas 4. Butter a 20 x 30cm cake tin and line with baking parchment. Tip the butter, sugar and vanilla into a large bowl and beat with an electric whisk for 4-5 mins until pale and fluffy. Or, do this in a stand mixer. Add the eggs, one at a time, beating well between each addition. Fold in the flour, baking powder, milk and lemon zest using a rubber spatula until smooth.

Pour the batter into the prepared tin and level the top with the back of a spoon. Bake for 25-30 mins until a skewer inserted into the middle comes out clean. If it’s not ready, check every 5 mins to ensure it doesn’t overbake. Leave to cool for 10 mins in the tin, then transfer to a wire rack to cool completely.

Meanwhile, make the icing. Put the raspberries or blueberries into a small heatproof bowl along with the lemon juice. Microwave for 1 min, stirring halfway through, until softened. Or, do this in a small pan over a low heat. Roughly break up the berries with a fork to release the juices, then press the crushed berries through a sieve into a small bowl to collect the seedless juice.

Tip the icing sugar into a large bowl and pour over the berry juice. Whisk well until you have a thick but spreadable icing – if it’s too thick, add 1 tsp water at a time until you reach the desired consistency. Add a drop of pink food colouring gel for a brighter colour, if you like. Spread the icing over the cooled cake, then immediately scatter over the coconut or sprinkles. Leave to set for 30 mins, then slice and serve.