Preheat the oven to 375 (F), and line a muffin tin with muffin cases.

Using a handheld electric whisk or a freestanding electric mixer with a paddle attachment, beat 6 tablespoons butter, 1 1/3 cup sugar, 1 1/2 cups flour, 1/4 teaspoon salt, and 1 tablespoon baking powder on low speed until the ingredients are well incorporated and have the texture of fine breadcrumbs.

Break 2 eggs into a Pyrex measuring cup, then add 1 cup whole milk and 1/2 teaspoon vanilla and whisk together by hand.

With the mixer running on a low speed, slowly pour three-quarters of the wet ingredients into the flour and butter mixture. Once everything has been mixed together, scrape down the sides of the bowl to pick up an ingredients that were missed, then add the rest of the milk mixture and continue mixing the batter until it is smooth and even.

Divide the batter between the paper cases, filling each case with 2 tablespoons of batter (or, filling each up to two-thirds full).

Bake for 18-20 minutes in the preheated oven until well risen and the tops bounce back when touched. Leave to cool slightly before removing them from the tin, then place on a wire rack to cool completely while you make the coffee soaking syrup.

Pour 1 cup coffee and 5 tablespoons Kahlua into a saucepan and whisk in 3 tablespoons granulated sugar.

Place the pan on your stovetop and bring to a boil, allowing the liquid to reduce by about half the pot, then remove from heat and set aside to cool.

Using a handheld electric whisk, beat together 14 oz. mascarpone cheese and 3 1/2 tablespoons Kahlua until smooth

Pour 1 1/3 cup heavy whipping cream in a separate bowl, adding 1/3 cup confectioner's sugar and using a handheld electric whisk to whip together until the mixture forms soft peaks.

Fold the whipped cream into the mascarpone mixture, making sure the mascarpone and the cream is fully incorporated.

Pour approximately 1 teaspoonful of the Coffee Soaking Syrup over each cut-out piece of the sponge, as well as another teaspoon into the hollow of each cupcake.

Fill each hollow to about halfway with the Mascarpone Cream Frosting, then place the cut-out pieces of the cupcake back on top of the hole, covering the filling and, if necessary, trimming the cupcakes pieces to fit.

Lastly, top the cupcakes with the remaining mascarpone cream frosting (I used about a tablespoon for each cupcake), and dust lightly with espresso and cocoa powder.