1. Whisk together the flour, cocoa powder, baking soda, and salt in a medium bowl.

2. In a large bowl, beat the butter, brown sugar, and granulated sugar until light and fluffy.

3. Add the eggs one at a time, then mix in the vanilla extract.

4. Gradually add the dry ingredients to the wet mixture and mix just until a thick dough forms.

5. Scoop the dough into equal portions onto a parchment-lined baking sheet, spacing them apart.

6. Bake at 350°F for 9 to 11 minutes, until the edges are set and the centers are still slightly soft.

7. Let the cookies cool on the pan for 5 minutes, then transfer them to a wire rack to cool completely.

8. For the filling, beat the butter until smooth, then mix in the powdered sugar, peppermint extract, and heavy cream until fluffy.

9. Add pink food coloring if desired and mix until the color is even.

10. Match the cookies into pairs of similar size.

11. Spread or pipe the filling onto the flat side of one cookie, then top with a second cookie.

12. Roll the filling edges in crushed candy canes and top with mini chocolate chips if desired.

13. Chill the assembled cookies for 15 to 20 minutes before serving.