In a large bowl using a hand-held or stand mixer fitted with a paddle attachment, beat the cannabutter, granulated sugar, and brown sugar together on medium high speed until fluffy and light in color. On high speed, beat in the egg, vanilla extract, and peppermint extract. Scrape down the sides and up the bottom of the bowl and beat again as needed to combine.
In a separate bowl, whisk the flour, cocoa powder, baking soda and salt together until combined. With the mixer running on low speed, slowly pour into the wet ingredients. Beat on low until combined. The cookie dough will be quite thick. Switch to high speed and beat in the milk, then the chocolate chips. The cookie dough will be sticky. Cover dough tightly with aluminum foil or plastic wrap and chill for at least 3 hours and up to 3 days.
Remove cookie dough from the refrigerator and allow to sit at room temperature for 10 minutes. If the cookie dough chilled longer than 3 hours, let it sit at room temperature for about 20 minutes.
Preheat oven to 350°F (177°C). Line large baking sheets with parchment paper or silicone baking mats. Set aside.
Scoop and roll dough, 1 heaping Tablespoon of dough each, into balls. Arrange 2-3 inches apart on the baking sheets. The cookie dough is sticky. Bake the cookies for 11-12 minutes or until the edges appear set and the centers still look soft. Allow to cool for 5 minutes on the cookie sheet. The cookies will slightly deflate as they cool. Transfer to cooling rack to cool completely before frosting.