Preheat the oven to 350°F. Line two standard muffin pans with 24 cupcake liners and set aside.

In a large mixing bowl, combine (1) 15.25 ounce box white cake mix, 1 cup whole milk, ½ cup vegetable oil, 4 large egg whites, and 1 teaspoon pure vanilla extract. Beat with a hand mixer or stand mixer on medium speed for about 2 minutes, until the cake batter is smooth and creamy.

Divide the cake batter evenly between two medium bowls. In a small bowl, dissolve 2 teaspoons espresso powder with 1 tablespoon hot water. Stir this espresso mixture into one bowl of batter until fully combined. You will now have one vanilla batter and one espresso batter.

Spoon about 1 tablespoon vanilla batter into each cupcake liner, then add about 1 tablespoon espresso batter on top. Use a toothpick or knife to gently swirl the two batters together. Fill the liners about two thirds full.

Bake the cupcakes for 16 to 18 minutes, or until a toothpick inserted in the center comes out clean. Allow the cupcakes to cool completely before filling.

To make the Crema al Mascarpone filling, bring a small saucepan of water to a gentle simmer over medium heat. While the water is heating, place 4 large egg yolks and ½ cup granulated sugar into a heat-safe bowl and whisk until smooth. Set the bowl over the saucepan, making sure the bottom of the bowl does not touch the water. Whisk constantly for 5-7 minutes, until the mixture thickens slightly and reaches about 160°F.

Remove the bowl from the heat and allow the mixture to cool to room temperature. Once cooled, whisk in (1) 8-ounce tub mascarpone cheese and 1 teaspoon pure vanilla extract until smooth and creamy.

In a separate bowl, whip ½ cup cold heavy cream until stiff peaks form. Gently fold the whipped cream into the mascarpone mixture until fully combined and smooth.

Using a cupcake corer or small knife, remove the center from each cupcake. Pipe about 1 tablespoon crema al mascarpone filling into the cavity of each cupcake.

Chill the filled cupcakes in the refrigerator for about 30 minutes so the filling can set.

To make the mascarpone frosting, place 8 ounces cold mascarpone, 2 tablespoons cold heavy cream, 1 teaspoon pure vanilla extract, and ⅛ teaspoon kosher salt into a large bowl. Beat with a mixer until just blended. Gradually add 2¼ cups powdered sugar, beating until the frosting is thick and smooth. If the frosting feels too stiff to spread or pipe, add a small splash of cream.

Pipe or spread the mascarpone frosting over each cupcake. Finish with a light dusting of unsweetened cocoa powder just before serving.