Line two baking sheets with parchment paper and set aside.
In a medium-sized bowl, whisk the flour, oats, baking soda, baking powder, and salt together. Set aside.
In the bowl of a stand mixer, cream the butter and sugars together for 2-3 minutes. Add the egg, yolk, and vanilla extract, beating until everything is combined well.
Little by little, add the dry ingredients to the butter/sugar in the stand mixer. Mix until the flour mixture is incorporated.
Using a cookie scoop, portion the cookie dough onto the prepared cookie sheets. Gently push a few M&Ms into the tops of the dough balls.
Chill the dough for at least 30 minutes, and up to overnight.
Preheat the oven to 350 degrees F.
Bake for 15-20 minutes, depending on how brown you'd like the cookies to be.