Whisk together the flour, cocoa powder, baking soda, baking powder, and salt in a large bowl and set aside.
Using a large bowl and hand mixer or stand mixer fitted with paddle attachment, cream together the butter and sugar for 2-3 minutes until fluffy. Add the egg and vanilla extract and beat on medium speed for 1-2 more minutes.
With the mixer on low, add the dry ingredients into the wet ingredients in thirds. Mix slowly just until dough is formed.
CHILL dough for 30 minutes.
Preheat oven to 350 degrees. Line two large baking sheets with parchment paper or silicone baking mats. Set aside.
Roll the dough into small (about two teaspoons) balls and place on prepared baking sheets. Press dough down slightly to flatten.
Bake 6-8 minutes. Allow cookies to cool on pan for 5 minutes before removing to cool on a wire rack.
For the filling:
In a large bowl if using hand mixer, or bowl of stand mixer fitted with paddle attachment, cream together the cream cheese and butter for 2 minutes until smooth.
Add the mint extract and powdered sugar, and beat for 2-3 more minutes until well combined.