Preheat oven to 350°F. Line two baking sheets with parchment paper and set aside.
In a stand mixer fitted with a paddle attachment, beat the butter, granulated sugar, and brown sugar for 2-3 minutes until creamy and light.
1 cup salted butter, softened, 1 cup granulated sugar, 1/2 cup dark brown sugar
Add the vanilla and eggs, then beat again, making sure to scrape down the bottom and sides of the bowl.
1 teaspoon vanilla, 2 large eggs
Mix in the flour, cornstarch, baking soda, and salt just until combined. It's okay if some streaks of flour remain.
3 cups flour, 1 Tablespoon cornstarch, 1 1/2 teaspoons baking soda, 3/4 teaspoon kosher salt
Stir in the Andes mint pieces and dark chocolate. If you didn't buy a extra box of Andes mints for chopping and pressing into the tops of the cookies, you might want to set aside 1/4 cup of the Andes mint pieces for pressing into the tops of the cookies after baking.
10 ounces Andes creme de menthe baking chips*, 1 cup dark chocolate chips
Use a cookie scoop to drop balls of dough onto the prepared baking sheets, spacing them a couple inches apart. Bake for 10-11 minutes, just until the edges are set but the middle still looks slightly under baked and even a bit shiny in the center. The cookies will continue to set up on the baking sheet after they are taken out of the oven.
Gently press a few extra pieces of Andes mints and dark chocolate into the tops of each cookie. This is a vanity move, but I love cookies that look extra pretty and this is my trick to making them that way! These cookies are SO GOOD when warm and the chocolate is still all melty from the oven.