Cream butter and sugar in a bowl with an electric mixer, then add eggs, vanilla and zest and mix to blend.
Add dry ingredients, milk and lemon juice alternately and fold in with a spatula. Pour batter into baking cups and bake for 20 minutes at 350°F.
Remove center of baked cupcakes and fill with lemon curd.
Place mascarpone, cold heavy cream and powdered sugar in a bowl and beat with an electric mixer on medium speed for about 3 minutes until the frosting is thick and firm.
Decorate the top of the cupcakes with a piping bag, add a slice of lemon and some zests.
Enjoy these lemon cupcakes.