Heat oven to 350° and prepare cookies sheets by spraying with cooking spray, lining with parchment paper, or using a silpat liner.
In the bowl of a stand mixer, or use a mixing bowl and handheld mixer, beat together the softened butter, granulated sugar, and brown sugar until combined. About 1-2 minutes.
Add the egg and vanilla extract. Beat until combined.
In a separate smaller bowl, add the flour, dry pudding mix, and baking soda. Stir with a whisk to break up any clumps. Add the dry ingredients, 1 cup at a time, into the wet mixture and beat together just until blended each time.
Mix in the chocolate chips and m&m's just until combined.
Take about 2-3 tablespoons of dough and roll into a ball (should look about the size of a golf ball). Repeat until dough is gone. Place dough balls onto a plate and let freeze for 5-10 minutes before baking.
Remove 12 dough balls from freezer and place on the cookie sheet. Bake for 11-14 minutes.
Let cool on the cookie sheet for 10 minutes and then remove cookies to a cooling rack to cool completely. If wanted, gently press a few m&m's on top of the cookies immediately when they come out of the oven.
Repeat with remaining cookies! Eat a cookie warm with milk, it's delicious!