In a medium bowl, whisk together flour, cocoa powder, espresso powder, salt, and cacao nibs. Set aside.

In the bowl of a stand mixer, cream together the butter and sugar on medium speed for 5 minutes, until pale and fluffy, scraping down the bowl as needed. Add vanilla and mix to incorporate. Add half the flour mixture and mix on low speed until incorporated. Scrape down the sides of the bowl, add remaining flour mixture, and mix again. Then turn mixer up to medium speed and mix for 2 minutes.

Lay a 15” square piece of parchment paper on a baking sheet and place shortbread dough in the center. The dough will be very soft (buttery!). From the bottom side of the parchment (so your hands don’t touch the dough), gently form the dough into a rough shaped ball. Top dough with another 15” square piece of parchment and use the bottom of a pan to gently press down on the parchment covered dough, until dough is 1/4” thick and about 11” in diameter. Use a rolling pin to gently even out any difference in thickness. Place pan with dough into refrigerator to chill for at least 1 hour.

Preheat oven to 325°. Prepare two baking sheets with parchment paper and set aside.

Remove top layer of parchment paper from chilled dough and set aside. Try to work quickly, as the dough gets softer the longer it is out. Cut dough into rounds with a small round cookie or biscuit cutter (mine is 1-3/8” in diameter). If your cookie cutter starts to get sticky, dip the edges in a small plate of cocoa powder in between cuts. Place rounds on prepared cookie sheet about 1” apart and bake for 12 to 14 minutes, or until firm. Let cool on pan 1 to 2 minutes and then remove to wire rack to cool completely.

While first pan of shortbread rounds are in the oven, form the remaining dough into a ball again, with your hands on the underside of the parchment. Place saved piece of parchment on top of the dough and flatten again to 1/4” thickness. Place in refrigerator to chill again. Cut and bake according to previous instructions.

In the bowl of a stand mixer fitted with a paddle attachment, whip butter on medium speed until pale and fluffy, about 5 minutes, occasionally scraping down sides of bowl. Add powdered sugar, heavy cream, and peppermint extract, and mix on low until combined. Increase mixer speed to medium-high and beat until very light and fluffy, about 3 to 5 minutes, occasionally scraping down the sides of the bowl.

For a neat and tidy dollop of buttercream on the shortbread rounds, use a piping bag fitted with a large plain tip to place buttercream onto the center of each round, about 1 teaspoon of buttercream each. Then use the back side of a small spoon to place an indentation in the center of the frosting. Fill indentation with crushed peppermint candy. If you prefer to not use a piping bag, simply use a small spoon or spatula to spread buttercream onto each shortbread round, and then sprinkle with crushed peppermint candy.