Preheat oven to 350 degrees. Line cupcake tins with paper baking cups.
In the bowl of a stand mixer fitted with the paddle attachment, mix together the egg, egg whites, oil, buttermilk, Greek yogurt or sour cream, and vanilla.
Sift the cake mix over the wet ingredients, and stir on low for 30 seconds, then beat on medium for 2 minutes.
Pour half of the cake batter into another bowl and set aside.
Take the remaining cake batter, and divide it among the baking cups (each should be filled about a third of the way).
Stir the coffee into the reserved cake batter just until evenly combined. Spoon it on top of the white cake in the baking cups.
Bake for 16 to 18 minutes. When done, let the cupcakes cool in the tins for 5 to 10 minutes, then remove and let cool completely on cooling racks.
To make the filling, beat together the mascarpone cheese, 1/2 cup powdered sugar, coffee and Marsala wine or rum until thoroughly combined.
Remove the center of each cupcake (see this blog for 3 different methods). Place the mascarpone cheese filling in a pastry bag fitted with a medium round tip and pipe some of the filling into each cupcake.
To make the icing, place the cream cheese and the powdered sugar in the bowl of a stand mixer fitted with the whisk attachment.
Whisk on medium speed until smooth, then whisk in the vanilla. Turn the mixer speed to low and gradually add the heavy cream. Once the cream is fully incorporated, turn the speed to medium-high (around speed 6 on a KitchenAid) and whip until stiff peaks form.
Place the icing in a pastry bag fitted with a large round tip and pipe onto each cupcake.
Store cupcakes in the refrigerator. Just before serving, sift cocoa powder over top of the icing.
* – I dissolved 2 tsp of instant coffee in ½ cup boiling water, and measured out the coffee for both the cake and the filling from that.
** – If you don't want to use wine or liquor, simply use an even tablespoon of strong coffee, or replace the teaspoon of wine or liquor with 2 tsp of rum extract.
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