Make the Cupcakes:

1. Preheat the oven to 350°F (175°C) and line a muffin tin with cupcake liners.
2. In a bowl, whisk together flour, baking powder, baking soda, and salt; set aside.
3. In a large bowl, beat the butter and sugar until light and fluffy.
4. Add eggs one at a time, mixing well after each addition. Stir in vanilla extract.
5. Alternately add the dry ingredients and buttermilk, mixing until just combined.
6. Fill cupcake liners 2/3 full with batter.
7. Bake for 18-20 minutes, or until a toothpick inserted in the center comes out clean.
8. Let cupcakes cool completely before adding the coffee soak.

Prepare the Coffee Soak:

1. Brew strong coffee or espresso and let it cool.
2. Stir in coffee liqueur (if using).
3. Using a fork or skewer, poke small holes in the top of each cupcake.
4. Brush the coffee mixture over each cupcake and let it absorb.

Make the Mascarpone Frosting:

1. Whip heavy cream until stiff peaks form.
2. In a separate bowl, beat mascarpone cheese, powdered sugar, and vanilla until smooth.
3. Gently fold the whipped cream into the mascarpone mixture until fully combined.

Assemble the Cupcakes:

1. Pipe or spread mascarpone frosting onto each cupcake.
2. Dust with cocoa powder and top with chocolate shavings if desired.