- Preheat the oven to 350°F. Line a 12-cup muffin pan with cupcake liners; set aside. If you have a second muffin pan, line 4 more cups with liners, if not, simply bake the first batch and then reuse the pan for the rest of the batter. (We found that it fills 12 perfectly.)
- In a medium bowl, whisk together the cocoa powder, flour, baking soda, baking powder, and salt; set aside.
- In a large bowl, whisk together the eggs, sugar, oil, vanilla, and coffee mixture until smooth.
- Add in half the dry ingredients to the wet ingredients, then half the buttermilk, mixing until smooth. Repeat with remaining dry ingredients and buttermilk. Add in chocolate chips and stir until just combined.
- Pour batter into cupcake liners, filling about ⅔ of the way. Bake 18-20 minutes until a toothpick inserted in the center comes out clean. Remove from oven and let cool completely.
- Make frosting: in a small bowl, combine the matcha powder and milk and stir until a smooth paste forms. It is important that you get rid of any clumps as best you can. In a mixing bowl, beat together the butter until smooth. Add in icing sugar and matcha mixture and beat until thickened. Transfer to a piping bag and frost the fully cooled cupcakes. Top with mini chocolate chips, if desired.