Zest and juice the lemons into a saucepan. Dice the butter and add to the pan, along with the sugar. Place the pan over a medium heat and allow the butter to melt. Reduce the heat and then one at a time, whisk in the eggs and the yolks. Continue whisking until you have a thick mixture that resembles custard and coats the back of a spoon. Remove from the heat and allow to cool.
While the lemon curd is cooling, prepare the meringue.
Preheat the oven to 120'C.
Place the egg whites and sugar in a large bowl over a pan of simmering water. Whisk together until frothy and slightly warm. Remove from the heat and continue whisking until firm. Transfer the mixture to a piping bag fitted with a star-shaped nozzle.
Spread the cooled lemon curd over the vanilla cupcakes and then pipe the meringue on top creating a swirl pattern. Leave for 10 minutes to allow to dry slightly and then bake in the oven for 40 minutes or until the meringues are firm and crisp to the touch.
«Take care not to over heat the egg whites over the pan of water - remove the bowl as soon as you start to feel the heat come through.»