• Preheat the oven to 350 degrees F and prepare a standard cupcake pan with cupcake liners.
• In a large mixing bowl, cream the butter sugar and light brown sugar until light in color and fluffy, 3 to 4 minutes. Add the sour cream and vanilla extract and mix until well combined. Add 1 of the egg whites and mix until well combined. Add the remaining 2 egg whites and mix until well combined. Scrape down the sides of the bowl as needed to be sure all the ingredients are well incorporated.
• Combine the flour, baking powder, cinnamon and salt in a medium bowl, then combine the milk and water in a small measuring cup. Add half of the flour mixture to the batter and mix until well combined. Add the milk mixture and mix until well combined. Add the remaining half of the flour mixture and mix until well combined. Scrape down the sides of the bowl as needed to be sure all of the ingredients are well incorporated.
• Fill the cupcake liners about halfway with batter. Bake the cupcakes for 15 to 17 minutes, or until a toothpick inserted comes out with a few crumbs. Remove the cupcakes from the oven and allow them to cool for 2 to 3 minutes in the pan, then transfer them to a cooking rack to finish cooling.

To make the frosting:

• Beat the mascarpone cheese, powdered sugar and vanilla extract together on medium-low speed until smooth. Do not overbeat or mix on high, or the frosting can get thin and watery (Mascarpone separates when overmixed.) Mix until just combined.
• Pipe the frosting onto the cupcakes and top with mini chocolate chips. Sprinkle with confectioners' sugar and store in the refrigerator until you are ready to serve. Serve at room temperature. These cupcakes are best eaten within 2 to 3 days.