For the Cupcakes:

1. Preheat your oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners.
2. In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.
3. In a separate large bowl, cream together the softened butter and granulated sugar until light and fluffy (about 2-3 minutes).
4. Add the eggs, one at a time, beating well after each addition. Stir in the vanilla extract.
5. Gradually add the dry ingredients to the wet ingredients, alternating with the milk, beginning and ending with the dry ingredients. Mix until just combined.
6. Divide the batter evenly between the muffin cups, filling each about 2/3 full.
7. Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Let the cupcakes cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.

For the Coffee Soak:

1. While the cupcakes cool, combine the cooled espresso or coffee and coffee liqueur (if using) in a small bowl or cup.
2. Once the cupcakes are completely cooled, gently poke several holes in each cupcake with a toothpick or fork.
3. Spoon the coffee soak over each cupcake, allowing the liquid to soak in.

For the Mascarpone Frosting:

1. In a chilled mixing bowl, beat the heavy cream with an electric mixer until soft peaks form.
2. In a separate bowl, whisk together the mascarpone cheese, powdered sugar, and vanilla extract until smooth.
3. Gently fold the whipped cream into the mascarpone mixture until well combined and smooth.
4. Frost the cooled, soaked cupcakes with the mascarpone frosting using a piping bag or an offset spatula.

Garnish:

1. If desired, sprinkle the cupcakes with unsweetened cocoa powder and top with chocolate shavings for a beautiful finishing touch.