Preheat oven to 350° F. In the bowl of a stand mixer, combine dry ingredients (flour, sugar, cocoa powder, baking soda, and salt). Mix briefly to combine.
Add melted butter and eggs and beat until combined. Add half the coffee, mix to combine. Add the second half of the coffee and beat until smooth.
Divide batter evenly among greased or paper-lined cupcake pans. Bake 18-22 minutes, or until a toothpick inserted in the center of the cupcakes comes out clean. Cool cupcakes completely on a wire rack.
For Buttercream:
In a medium heatproof bowl, combined egg whites and sugar. Place over a small saucepan of simmering water, taking care that the water doesn't come into contact with the bowl.
Cook mixture over medium-high heat, stirring often, until it reaches 160° F.
Once mixture has come to temperature, transfer to the bowl of a stand mixer. Beat on medium-high speed using the whisk attachment until bowl is nearly cool to the touch and mixture has doubled in volume, 10-12 minutes.
Add butter one piece at a time, allowing each piece to incorporate before adding the next. Keep mixing until buttercream is smooth. Add peppermint extract and mix to combine.
Cupcakes can be frosted with the buttercream once they are completely cooled. Top with crushed candy canes and crisp chocolate pearls, if desired.Enjoy!
Notes
Note on espresso powder: I've found it difficult to find espresso powder--especially one that isn't already hard as a rock--at my local grocery store. I use King Arthur Baking's brand, as it's very fine and made specifically for baked goods.Note on crisp chocolate pearls: I like using these little guys to jazz up baked goods. I can only ever find them online.