In a large mixing bowl, using a stand mixer or a hand mixer, beat the softened unsalted butter, granulated sugar, and light brown sugar together on medium-high speed until the mixture is light, fluffy, and pale in color. This takes about 2 to 3 minutes.

Add the eggs one at a time, beating well after each addition until fully incorporated. Scrape down the sides of the bowl as needed. Add the peppermint extract, vanilla extract, and a few drops of green food coloring if using. Mix on low speed until just combined.

In a separate medium bowl, whisk together the all-purpose flour, cornstarch, baking soda, and salt.

Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix.

Gently fold in the semisweet chocolate chips and the Andes mint baking chips using a rubber spatula.

Cover the bowl with plastic wrap and refrigerate the cookie dough for at least 2 hours, or preferably overnight.

Preheat your oven to 350°F (175°C). Line two large baking sheets with parchment paper.

Scoop the chilled dough into 1.5 tablespoon-sized balls and place them about 2 inches apart on the prepared baking sheets.

Bake for 10 to 12 minutes, or until the edges are golden brown but the centers still look slightly soft and underbaked.

Let the cookies cool on the baking sheet for 5 to 10 minutes before transferring them to a wire rack to cool completely.