In a large mixing bowl, whisk together the all-purpose flour, unsweetened cocoa powder, and baking soda until thoroughly combined. Set aside.

Preheat your oven to 350°F (175°C).

In a separate bowl, beat the softened butter and granulated sugar until light and fluffy, about 2-3 minutes. Add the egg and peppermint extract, mixing until well combined.

Gradually add the dry ingredients to the butter mixture, mixing on low speed until just combined.

Using a cookie scoop or tablespoon, drop even mounds of dough onto a lined baking sheet, about 2 inches apart.

Bake for 10-12 minutes, until the edges are set and tops are slightly cracked. Let cool on the sheet for 5 minutes before transferring to a wire rack.

While cookies cool, beat together the softened butter and powdered sugar for the filling. Gradually mix in the heavy cream and mint extract until smooth.

Spread a generous layer of filling on the flat side of half the cookies, then top with another cookie.

Serve and enjoy on a cheerful holiday platter.