Preheat oven to 350°F and line a muffin pan with paper liners.
In a bowl, whisk together the flour, baking powder, and salt and set aside.
In a seperate bowl using a stand or hand held mixer, beat the butter and sugar together until light and fluffy, 2-3 minutes.
Add the egg and egg white one at a time to the butter/sugar mixture, beating well after ech addition.
Add the vanilla extract.
Using a low speed, add the flour mixture in 3 additions, alternating with the milk, starting and ending with flour. Scrape down bowl as needed.
Beat on high speed until no traces of flour remain, about 30 seconds. Do not overbeat.
Divide batter evenly into prepared muffin cups, filing each about 3/4 full.
Bake until lightly golden and toothpick inserted in center comes out clean 18-20 min.
Let cupcakes cool in muffin pan for 5 min, then remove them to a cooling rack and let them cool completely. About an hour.
When your ready to fill the cupcakes take out the Marscapone Cheese to soften a bit.
Once cooled, using a knife or a frosting tip, gently remove a circle part of the center of the cupcake, making sure you do not go all the way through to the bottom. Set removed part aside.
Fill cupcake with about 1/4 tsp of lemon curd
Add the removed cupcake top back onto the cupcake, pressing gently.