Fold in the self-rising flour, then add the milk and mix until just combined.
2 cups self-rising flour, 4 tablespoons milk
Divide the batter between the liners. Bake for about 20 minutes, or until a toothpick inserted in the center comes out clean.
Pierce the tops of the warm cupcakes with a skewer. Brush the coffee syrup over the cupcakes until it is used up. Let the cupcakes cool completely.
Frosting
Mix the mascarpone with the confectioners sugar, espresso powder, and coffee liqueur until smooth.
¾ cup mascarpone, ⅓ cup confectioners sugar, 1 teaspoon espresso powder, 1 ½ tablespoon coffee liqueur
In another bowl, whip the cold heavy cream until stiff.
⅔ cup heavy cream
Stir one-third of the whipped cream into the mascarpone mixture. Gently fold in the rest.
Pipe or spoon the mascarpone topping onto the cooled cupcakes.
Dust with Dutch-process cocoa powder before serving.
1 tablespoon Dutch unprocessed cocoa
NOTES
1. Can I make the cupcakes a day ahead? Yes. Bake the cupcakes and brush them with syrup. Keep them covered and add the mascarpone topping the next day.2. My mascarpone topping looks lumpy. What should I do? Let the mascarpone sit at room temperature for about 15 minutes before mixing. Keep the heavy cream cold and fold it in gently.3. Can I skip the liqueur? Yes. Replace it with extra coffee for an alcohol-free version.4. How much syrup should I brush on each cupcake? Use enough to moisten the top well, but stop before the cupcake turns soggy.5. Can I use a piping bag or just spoon on the topping? Both work. A piping bag gives a neater party look, but spooning is fine too.6. Storage
Fridge: Store topped cupcakes covered in the refrigerator for up to 2 days.
Serving: Let the cupcakes sit at room temperature for 15 to 20 minutes before serving, so the topping softens slightly.
Freezer: Freeze only the unfrosted cupcakes for up to 1 month. Add the syrup and topping after thawing.
Make-ahead: Bake and syrup the cupcakes 1 day ahead. Make the mascarpone topping fresh for the best texture.