Preheat oven to 350 degrees. Make the cupcakes: Whisk together flour, baking powder, baking soda, and salt. Pour water over espresso powder; let cool. Combine espresso with milk. Beat butter and granulated and brown sugars with a mixer on medium speed until pale and fluffy, about 3 minutes. Add eggs, 1 at a time, beating well after each addition. Beat in flour mixture in 3 additions, alternating with espresso-milk mixture, beginning and ending with flour (batter may look broken).
Fill 15 cups (of two 12-cup muffin tins) three-quarters full. Bake until a toothpick inserted into the centers comes out clean, 20 to 22 minutes. Let cool; turn out cupcakes from tins.
Make the frosting: Whisk together cream and confectioners' sugar until medium peaks form. Add whiskey; whisk until slightly stiff peaks form.
Top each cupcake with 2 tablespoons frosting; dust with espresso powder.