2. Line a cup cake or muffin tray with paper cases.
3. Beat together the butter and caster sugar until light and fluffy. Add the eggs a little at a time.
4. Fold in the flour.
5. Spoon the mixture into the paper cases, half full.
6. Bake in the oven until golden brown and springy to touch or test using a skewer, if it comes away clean the cakes are ready. Leave them to cool on a wire rack.
7. Meanwhile prepare the icing, begin by beating the butter and icing sugar until pale and well mixed, ideally using an electric mixer. Add the yogurt and continue to beat on medium to high speed until the icing is fluffy. The longer you beat the lighter the icing.
8. Spoon the icing into a piping bag fitted with a star piping nozzle in a circular motion swirl the icing around each cake.