1. Start by stirring the espresso powder into 2 tablespoons of hot water until completely dissolved. Set it aside to cool slightly.

2. This little step is worth doing rather than adding dry espresso powder directly to the batter. It distributes the coffee flavor more evenly throughout the cupcakes.
3. Preheat your oven to 350°F (175°C). Line a 12-cup muffin pan with cupcake liners.
4. In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, and salt. You don't need to overwork the mixture. Just whisk everything together until evenly combined.
5. In a large bowl, whisk the melted butter, brown sugar, and granulated sugar until smooth. Add the eggs one at a time, whisking well after each addition. Stir in the vanilla, mashed banana, milk, and cooled espresso mixture. The batter may look slightly uneven because of the mashed banana, and that's completely fine.
6. Add the dry ingredients to the banana mixture. Fold gently with a spatula until just combined. Be careful not to overmix. A few tiny streaks of flour disappearing into the batter are better than beating it until perfectly smooth. Overmixing can make the cupcakes dense instead of soft.
7. Divide the batter evenly among the 12 liners, filling each about two-thirds full. Bake for 18–22 minutes, or until the tops spring back lightly when touched and a toothpick inserted into the center comes out clean or with a few moist crumbs.
8. Let the cupcakes cool in the pan for about 5 minutes, then transfer them to a wire rack to cool completely. Don't rush this part. Warm cupcakes can cause buttercream to melt right off the top.

Make the Espresso Buttercream

1. While the cupcakes cool, prepare the frosting. Dissolve the espresso powder in 1 tablespoon of hot water and let it cool for a few minutes.
2. Beat the softened butter until smooth and creamy, about 2–3 minutes. Gradually add the powdered sugar and continue beating until fluffy. Add the espresso mixture, vanilla, and a pinch of salt. Beat again until smooth.
3. If the frosting feels too thick, add the cream or milk one teaspoon at a time until you reach a soft, pipeable consistency. Or if it becomes too loose, add a little more powdered sugar.

Frost and Decorate

1. Once the cupcakes are completely cool, pipe the espresso buttercream over each one.
2. For a simple finish, sprinkle the tops with a little cinnamon. For a more coffeehouse-inspired look, add a small banana chip or chocolate-covered espresso bean.
3. You can also drizzle a tiny amount of melted chocolate over the frosting for an extra-dessert kind of finish.