Preheat the oven to 180 degrees/gas mark 4. Cream the butter and sugar together in a mixing bowl. Add the eggs and the flour gradually, folding as you go.
Add the zest and juice from half a lemon and mix well.
Prepare 12 cupcake cases in a tin. Gradually add the mixture until you have filled the cases three quarters of the way up (depending on how big you like your cupcakes). Place these in the oven for 15-20 minutes, or until golden brown.
Cool the cupcakes on a wire rack, and prepare your meringue. Whisk the egg whites using an electric whisk until stiff peaks form. Gradually add the caster sugar a tablespoon at a time, and continue whisking.
Cut a small indentation into the cupcake and fill with lemon curd.
Pipe the meringue onto the top of cupcake, using a round or star-shaped piping nozzle, and either brown with a blowtorch, or place back in the oven for five minutes until it has changed colour.