Preheat the oven to 350 degrees. Line two cupcake pans with paper liners.
Muddle the mint in a small bowl, then add to the freshly brewed coffee. Let steep for 15 minutes.
In a medium bowl, whisk together the eggs, buttermilk, applesauce, canola oil and vanilla.
In a large bowl, sift the flour and cocoa powder. Add in the sugar, baking powder, baking soda and salt.
After the 15 minutes of steeping, strain the coffee into the buttermilk mixture, discarding the mint leaves.
Pour the buttermilk mixture into the flour mixture and mix until combined.
Divide the batter into the cupcake pans, filling each ¾ of the way full.
Bake for 20 minutes.
Cool on a wire rack.
While the cupcakes are cooling, prepare the frosting by combining the butter and cocoa powder in the bowl of a stand mixer. Beat on medium speed for 3 minutes.
Add in the powdered sugar, 1 cup at a time, then add in the milk, vanilla and salt.
Transfer the frosting to a piping bag and pipe frosting on top of cooled cupcakes. Decorate cupcakes with additional fresh mint leaves if desired.