• Preheat the oven to 350°F and line a muffin tin with cupcake liners.

Make the Cupcakes:

• In a small bowl, whisk together the flour, baking powder and salt. Set aside for now.whisk
• In a larger bowl, beat the butter and granulated white sugar until light and fluffy.
• Add the milk, vanilla extract and eggs. Beat until incorporated.
• Gradually add the dry ingredients to the butter mixture and mix just until combined.
• Divide the batter in half.
• To one half, stir in a tablespoon of cocoa powder and a tablespoon of espresso powder until just combined.
• Divide the batter evenly among the cupcake liners, alternating between the batters, filling each about two-thirds full.
• Take a toothpick and swirl the two batters together to make a marble pattern.

Bake the Cupcakes:

• Bake for 18 to 20 minutes, or until a toothpick inserted into the center comes out clean.
• Let the cupcakes cool completely.

Make the Frosting:

• In a large bowl, beat the butter, mascarpone cheese, powdered sugar, vanilla extract, and salt together until thick and fluffy. Add more powdered sugar or milk if you need to thicken or thin the frosting.
• Pipe or spread the mascarpone frosting onto the cupcakes.
• Dust the tops with unsweetened cocoa powder just before serving.