Preheat oven to 160°C fan/180°C/350°F. Grease and line 2 6" cake tins (4 if you have them). Place the butter into the bowl of a stand mixer (or use a regular bowl and an electric whisk). Add the caster sugar and beat until light and fluffy. Beat in the eggs one by one, adding a spoonful of flour between each one.
The recipe for the cake layers is barely adapted from Primrose Bakery.