Preheat the oven to 350 F. Line 2 baking sheets with parchment paper or silicone baking mats.
Microwave the butter in a large, microwave-safe bowl for about 40 seconds. Butter should mostly melted.
Whisk the butter until it is completely melted.
Add the sugars; mix until well-combined.
Stir in peppermint extract, vanilla extract, and egg until incorporated.
Add the flour, cocoa powder, baking soda, and salt. Please read the recipe note about properly measuring flour.
Mix dough until just combined. Dough should be soft and a little sticky but not overly sticky.
Stir in the mini chocolate chips.
Place the crushed peppermint candy in a shallow dish.
Scoop out 2 tablespoons of dough and dip the top of each cookie in the peppermint candy. Don't roll the entire cookie.
Place 3 inches apart on baking sheet. You can see how I stagger the cookie dough in the picture above.
Bake for about 10-13 minutes, or until cookies are set. They will be puffy and still look a little underbaked in the middle.
Notes
Peppermint extract: It's important to use peppermint extract, not mint. Mint is more of a spearmint flavor (like mouthwash).
Measuring Flour: If you aren’t weighing your ingredients, I can’t recommend that enough. If you are using measuring cups, be sure to sift or stir the flour before measuring. Flour packs easily and using too much flour in cookies will give you dry, crumbly dough and cookies that don’t spread.
Chocolate Chips: I use mini semisweet chocolate chips. You can use regular chocolate chips if you prefer. You could even use white chocolate chips if you like.
Peppermint: I prefer to crush up a candy cane instead of using the pre-crushed peppermint candy for these cookies. The pre-crushed candies tend to have really small pieces that melt into the cookies (you can see some of the smaller pieces that have melted into the cookies in the photos).