Preheat oven to 350°F. Line two baking sheets with parchment and set aside.
Melt the butter in the microwave for about 30 seconds. The butter should just barely be melted.
Cream the melted butter and brown sugar together using a stand mixer or electric beater, about 2-3 minutes. Add in the vanilla. Scrape down the sides and bottom of the bowl and make sure everything is incorporated fully.
Add the egg and beat until just barely combined, about 10 seconds.
In a separate bowl, whisk together flour, cocoa powder, instant espresso powder, cornstarch, baking soda and salt.
Add the dry ingredients into the wet ingredients and mix for about 20 seconds, then add the chopped Andes Chocolate mints, and mix on slow until just combined. You don’t want to overwork the dough, so stop mixing when you can still see just a few streaks of flour. Then mix the rest of the way by hand using a spatula or your bare hands.
Scoop the dough into balls using a 1 ½ Tbsp ice cream/cookie scoop. Roll the balls in your hands to form nice, uniform balls.
Place on the prepared baking sheets and bake for 8-10 minutes. I found that 7-8 minutes was perfect for me. You want to underbake the cookies so they stay soft. Let them cool on the baking sheet for 5-10 minutes before transferring to a cooling rack to cool completely.
Melt the white chocolate. Dip half of the cooled cookie into the white chocolate and place on a parchment lined baking sheet. Sprinkle with your favourite festive sprinkles and allow to sit until the chocolate has hardened.