First mix butter and sugar together in a large bowl till creamy. In a separate bowl, beat the eggs with a splash of milk. Gradually add the eggs to the sugar and butter mixture, stirring well.
Add the flour and fold it in. Add the zest of 1 lemon and add the juice of half a lemon. Leave the other half aside later to be used for the topping
Spread the mixture evenly into a non stick 20cm cake tin, and place the tin in the already heated oven which should be set at 180 C / Gas 4.
Bake for 25 minutes or until skewer comes out clean. Leave the cake until it is completely cooled.
When the cake is cool, take it out of the tin and squeeze the juice of the half lemon that was left all over the top. Make sure it is squeezed evenly to make it taste even. Then sprinkle a lot of caster sugar over the top and leave for 1 hour so the juice soaks in.