Preheat the oven to 180°C, fan 160°C, gas 4. Line a 12-hole muffin tin with paper cupcake cases. In a large mixing bowl, use an electric whisk to beat the butter and caster sugar together until light and fluffy.
Beat in the eggs with a little of the flour, to stop the mixture curdling. Fold in the remaining flour with the vanilla extract, until you have a smooth mixture with no lumps. Divide the mixture evenly between the cupcake cases, filling each no more than two-thirds full. Bake for 20-25 minutes until a skewer inserted into the middle of a cake comes out clean. Transfer to a wire rack to cool.
To decorate, use an electric whisk to mix the butter and icing sugar until combined. Spoon on top of the cupcakes and smooth with a palette knife to create slightly domed tops.
Roll out the coloured ready to roll icing, then, using a 7cm round cutter, stamp out 12 discs and carefully place one on top of each cupcake. Use the icing trimmings, the writing icing and white chocolate buttons to create quirky faces. (Use the writing icing for finer details such as smiley mouths and the centres of the eyes, and use extra blobs to help fix the decorations in place.)
Cook’s tip: why not surprise everyone with some tasty hidden extras in the cakes? Before spooning the sponge mixture into the cases,divide it between two bowls and stir 100g mini marshmallows into one half and 75g baking additions raisins, hazelnuts and chocolate by Sainsbury’s into the rest. You’re sure to raise an extra smile or two!