Preheat the oven to 350 degrees Fahrenheit.
Line a mini cupcake tin with liners and set aside. In a medium mixing bowl, beat together the butter, sugar, egg, greek yogurt, brewed coffee and vanilla until well combined.
Beat in the flour, cocoa, baking powder and salt just until smooth.
Add to your prepared cupcake tin, filling about 3/4 of the way up. You should have 24 mini cupcakes.
Bake for 12-17 minutes or until a toothpick comes out clean.
Let cool in the tray for 10-15 minutes, then remove from the tray to finish cooling.
Top with chocolate or vanilla buttercream and enjoy!