Heat the oven to 180C/160C fan/gas 4 and line a 12-hole cupcake tin with paper or silicone cases. Put the butter and sugar in a large bowl and beat with an electric whisk until light and creamy. Pour in the egg, a little at a time, mixing well after each addition. Next, beat in the vanilla paste, then fold in the flour, baking powder and a pinch of salt until well combined. Spoon the mixture evenly between the cases. Bake for 15-20 mins until the tops are golden and firm to the touch at the edges. Leave to cool in the tin for 15 mins, then transfer to a wire rack to cool completely.

For the buttercream, beat the butter with an electric whisk until pale and fluffy in a clean, large bowl. Add the icing sugar, one spoonful at a time, mixing as you do. Beat in the vanilla. To decorate, transfer the buttercream to a piping bag fitted with a round or star nozzle. Pipe generous swirls on top of each cupcake. Will keep in an airtight container for up to three days.