Preheat oven to 350°F. Line two baking sheets with parchment paper.
In a small bowl combine flour, baking soda and salt. Set aside.
In a large bowl, using a hand mixer or stand mixer, beat butter and both sugars for 1-2 minutes, scraping the bowl as needed.
Add egg and peppermint extract and beat until combined.
Slowly add the flour mixture, beating until just combined.
Add 1 cup of mint chips/Andes/chocolate chips (the rest will be reserved for topping the cookies).
Scoop 2-tablespoon portions of dough and place them a couple inches apart on the baking sheets.
Bake the cookies for 9-11 minutes until the edges are just beginning to turn golden brown and the very center is still slightly underdone.
Rotate the baking sheets halfway through cooking time, if necessary.
While the cookies are still warm, use the remaining ½ cup mix-ins and nestle pieces into the tops of the cookies.
Place the baking sheets on wire racks and allow the cookies to cool completely.
