For the sponge:
125g caster sugar
100g unsalted butter
100g Greek yogurt
2 eggs, lightly beaten
250g self-raising flour
4 egg whites
2tsp baking powder
½tsp vanilla extract
Finely grated zest of two unwaxed lemons
For the topping:
50g icing sugar, sifted
2tbsp limoncello (or lemon juice)
Preheat the oven to 170C (fan 150C/gas mark 3) and set the shelf in the middle. Spray a 20cm round, loose-bottomed, deep cake tin with oil, line the bottom with baking parchment. Put the sugar, butter and yogurt into a food mixer or large bowl and beat like mad.
Next, add the two whole eggs and half of the flour and beat for a good few minutes, until the mixture is well blended and starts to look a little smoother.
Whisk the four egg whites until light and frothy then fold them into the mixture with the rest of the flour, the baking powder, vanilla extract and lemon zest and beat until you have a smooth batter. Finally, stir half of the blueberries through.
Pour the mixture into the tin. Arrange the remaining blueberries on the top in a few lines across the centre. Pop into the oven for about 25-30 minutes.
To make the topping, put the icing sugar into a small bowl. Stir in the limoncello (or lemon juice) to give a smooth, runny mixture to use once cake is cool.