Preheat your oven at 180 C.
Put the butter in your mixer and start mixing it untill it's soft and creamy.
Then add to it the sugar, the milk, and the eggs and beat. Last but not least add the flour, the baking powder, the salt, and the lemon peel.
Spoon the batter in the paper cases and bake it in the oven for about 20 minutes.
For the lemon curd start beating all the ingredients in a bowl. Then slowly heat them in a bain-marie being careful not to cook the egg. Keep on stirring with a lot of patience because it may take about 30 minutes.
If you see that your mixture is not getting any thicker add some icing sugar. It's ready when it's no longer liquid but creamy.
Of course you can buy it ready-made from the supermarket as well!
Before you serve your cupcakes make sure they have cooled down. With a knife cut the upper part and remove it but don't throw it away or eat it ;)
Put on your open cupcake a layer of mascarpone and one of lemon curd and reclose it. Some icing sugar and a slice of lemon and tehre you have the finishing touch!
(Store in the fridge for no longer than 2 days)