In a large bowl whip the egg whites until starting to foam. Then slowly drizzle in 2 tablespoons of sugar and continue to mix on medium speed until stiff peaks form, then set aside.
In another large bowl cream together the granulated sugar and butter until light and fluffy, make sure to scrape down the sides of the ball as you go to ensure everything is evenly incorporated.
Bake for 13-16 minutes, or until a toothpick inserted in the center comes out with only moist crumbs no wet batter, or if you gently press the top of the cupcake it bounces back immediately.
Once the cupcakes have completely cooled use a knife to cut a hole out of the center, you want it to be fairly deep but not all the way to the bottom. You basically just want the top part left to cover the ducle de leche filling.
Place dulce de leche in a piping bag with no tip or a medium round tip to easily fill the holes of the cupcakes, then place the "lid" piece of the cupcake back on top.