Preheat the Oven: Set the oven to 350°F (175°C) and line a muffin tin with cupcake liners.
Mix Dry Ingredients: In a bowl, whisk together flour, baking powder, baking soda, salt, and cinnamon.
Mix Wet Ingredients: In another bowl, beat together sugar, butter, and mashed bananas until smooth.
Add the Egg: Beat in the egg and vanilla extract until fully combined.
Combine Wet and Dry Ingredients: Gradually add the dry ingredients to the wet mixture, alternating with milk.
Fill the Tin: Spoon the batter into cupcake liners, filling each about ¾ full.
Bake the Cupcakes: Bake for 18-20 minutes or until a toothpick comes out clean.
Cool the Cupcakes: Let the cupcakes cool in the tin for 5 minutes, then transfer to a wire rack.
Make the Frosting: Beat together butter, powdered sugar, coffee, and vanilla extract until smooth and creamy.
Frost the Cupcakes: Spread or pipe the frosting over cooled cupcakes