To make the cupcakes: Preheat the oven to 180 C / Gas 4. Combine all the cupcake ingredients and beat until combined. Spoon into greased cupcake moulds about 2/3 full.
Bake in the preheated oven until a skewer inserted near the centre comes out clean, about 20 minutes.
To make the lemon filling: Combine lemon juice, lemon zest, sugar and egg yolks in a saucepan and cook over medium-low heat just until the first bubble appears on the surface, about 6 minutes. Remove from heat and whisk in the cold butter. Set aside to cool in the refrigerator.
To make the Italian meringue frosting: In a pan, heat sugar and water until dissolved. Boil rapidly until a single drop of syrup dropped into a glass of cold water forms a soft ball. Let cool.
Meanwhile, beat egg whites until stiff. Gradually pour cooled syrup over the egg whites, beating constantly. Continue to beat until thick and fluffy.
When cupcakes have cooled, remove some of the centre with a spoon or melon baller. (Discarded cake is the helpers' and chef's treat!) Fill the holes with lemon curd filling.
Pipe the frosting onto the filled cupcakes and allow to cool completely in the fridge. Before serving, put the cupcakes under a preheated grill, or use a kitchen torch to brown the meringue frosting. Again, allow to cool completely before serving. ENJOY!
Make it as a cake. use lemon curd as a filling between layers and frost all over with meringue.