Cupcakes: Preheat the oven to 180 degrees C. Line a cupcake tray with patty cups.
In a bowl, mix the flour, baking powder and salt. In the bowl of a food processor whisk the butter and sugar until creamy. Add the eggs one by one continuing to whisk then add the vanilla seeds, lemon zest, lemon juice and poppy seeds.
Add half of the flour mixture, then buttermilk and then the rest of the flour mixture. Mix.
Fill the patty cups with the mixture and bake in the oven for 20-25 minutes. Once the cupcakes are cooked, cool completely before topping with the icing.
Icing: In the bowl of a food processor whisk the mascarpone, icing sugar and vanilla seeds until you get peaks. Stir in 3 tablespoons of lemon curd and mix gently with a spatula. Refrigerate.
To Serve: Cut the top part off the cupcakes above the paper case. Cut the tops in half and set them aside. Put the icing on the cupcake then return the two half pieces, flat side down, leaving some space to add a little bit of lemon curd in the centre with a pastry bag.