Preheat oven to 350°F. Line a cookie sheet with parchment paper and set aside.
Add the butter, granulated sugar, and brown sugar to a large mixing bowl or large bowl of an electric stand mixer. Cream the ingredients together until light and fluffy, using a hand mixer or the paddle attachment on a stand mixer.
Add egg, egg yolk, and vanilla. Mix until well combined. Scrape down the side of the bowl as needed.
Add flour, baking soda, baking powder, and salt, mixing until just combined.
Stir in 1 cup of M&M's and chocolate chips.
Use a medium-sized cookie scoop, and scoop out the dough into balls, place them on the cookie sheet 1 inch apart. Use the remaining ½ cup of the M&M's and press them on top of the dough balls.
Bake for 10-12 min. Remove from the oven and allow to cool on a cooling rack for 5 min.