• Preheat the oven to 350ºF (180ºC). Line two large baking sheets with parchment paper or silicone baking mats.
• Combine the flour, cocoa, baking powder, baking soda, and salt in a bowl. Set aside.
• Using an electric hand mixer or a stand mixer, beat the butter, granulated sugar, and brown sugar on medium speed until smooth and creamy, 3 to 4 minutes. Scrape down the sides and bottom of the bowl as needed.
• Reduce the speed to low and add the flour mixture; mix until it resembles coarse crumbs.
• Add the chocolate chips and mix to distribute evenly.
• Add the milk and peppermint extract; mix until the dough comes together into a big ball.
• Scoop out about 1 1/2 to 2 tablespoons of dough for each cookie. Roll each portion into a ball and place it on the prepared baking sheets, evenly spacing them about 2 inches apart. Note: You can bake these cookies right away, but if you have time, refrigerate the dough for 30 minutes or up to 2 days for an extra chewy cookie.
• Bake for 10 to 12 minutes, or until the edges appear set, but still soft in the middle. When you remove the cookies from the oven, they will still look doughy, and that’s okay; they will continue to set as they cool.
• Cool on the baking sheets for 5 minutes, then transfer to wire racks to cool completely.

Decorate:

• Once cookies are completely cool, melt white chocolate in a microwave-safe bowl on 50% power in 30-second increments, stirring between intervals until melted and smooth.
• Dip half of each cookie in white chocolate, then transfer to parchment paper and sprinkle with crushed peppermint candies. Chill the dipped cookies to let the chocolate set for about 10 minutes.