Preheat the oven to 350 degrees F (175 degrees C). Line 2 cupcake pans with paper liners.
Mix espresso powder and hot water in a measuring cup until powder is dissolved. Set aside.
Whisk flour, cocoa powder, baking powder, baking soda, and salt together in a bowl until well combined.
Cream butter, brown sugar, and white sugar in a large bowl with an electric mixer until light and fluffy. Beat in egg until thoroughly combined. Mix in espresso mixture, vanilla, and peppermint extract. Add in 1/3 of the dry ingredients and mix until just combined. Mix in cooled coffee until just combined. Stir in another 1/3 of the dry ingredients until just combined. Mix in buttermilk until just combined. Stir in remaining dry ingredients until just combined. Do not overmix. Fold in chocolate chips.
Spoon batter into the prepared cups, filling each line just over 1/2 full.
Bake in the preheated oven until cupcakes spring back lightly when touched, 15 to 20 minutes. Cool a few minutes in the pan before removing to a wire rack to cool completely.
Make sure not to overfill your cupcakes liners, as these cupcakes rise substantially while baking.
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