Andes Mint Chocolate Cookies

Instructions

Start by creaming together the softened butter, granulated sugar, and brown sugar until they're fluffy and light in color, which usually takes about 2–3 minutes. Add the egg and vanilla extract, then beat until well combined. Remember to scrape down the sides and bottom of the bowl as needed.
In another bowl, whisk together the flour, cocoa powder, baking soda, and salt until everything's combined. While the mixer runs on low speed, slowly pour these dry ingredients into the wet mixture. Beat on low until they're combined. The dough will be thick. Then, mix in the milk on high speed until it's well incorporated. The dough will be thick and a bit sticky.
Cover the dough tightly and let it chill in the refrigerator for at least 2 hours, up to 3 days. This chilling step is really important because the dough is sticky.
Preheat your oven to 350°F (177°C) and line large baking sheets with parchment paper or silicone baking mats.
Once chilled, scoop and roll the dough into balls, about a heaping tablespoon each. Roll each ball in granulated sugar and place them 2–3 inches apart on the prepared baking sheets.
Bake the cookies for 10–12 minutes or until the edges appear set. Tip: If they aren't spreading much by minute 9, take them out of the oven and lightly tap the baking sheet on the counter 2–3 times. This helps them spread. Put them back in the oven to finish baking.
Let the cookies cool on the baking sheet for just 2 minutes. Then, press 1 Andes chocolate mint into the top of each warm cookie. Wait for 5 minutes before using a knife, icing spatula, or toothpick to gently swirl/spread the melted chocolate.

Move the "frosted" cookies to a cooling rack to cool completely. The cookies will slightly deflate as they cool. Andes chocolate sets in less than an hour, making it easy to store, stack, and transport the cookies.
Store any leftover cookies tightly covered at room temperature for up to 1 week.