Preheat the oven to 180°C/ Gas Mark 4.
Place the butter and WHITWORTHS CASTER SUGAR in a large mixing bowl. Using an electric whisk or wooden spoon, beat the butter and WHITWORTHS CASTER SUGAR together until the mixture is very pale in colour and fluffy.
Gradually beat the eggs into the creamed mixture, one at a time, until well combined. Sift the flour and baking powder into the bowl and using a large metal spoon, fold in lightly until no traces of flour remain.
Sit the ice cream cups on a baking tray and divide the mixture evenly.
Bake in the oven for 12-15 minutes, or until risen and golden, or until a skewer inserted into the centre of the cake comes out clean. Transfer to a cooling rack.
Beat the butter in a large bowl until soft using either an electric hand whisk, or a wooden spoon. Add half the WHITWORTHS ICING SUGAR and beat until smooth.
Add the remaining WHITWORTHS ICING SUGAR and one tablespoon of the milk and beat the mixture until smooth. Add additional milk if necessary to loosen the mixture. Finally, add the vanilla extract and continue to beat until fully combined.
Using a flower nozzle, fill a piping bag with the buttercream and pipe over the cooled cakes to resemble soft-whip ice cream.
Decorate and serve.