Preheat oven to 350-degrees and line three cookie sheets with parchment paper. Set aside.

In the bowl of a stand mixer, affixed with the paddle attachment, cream together the butter, brown sugar and white sugar on medium-high speed, until light and fluffy. Mix in the eggs and vanilla extract. Scrape down the sides of the bowl as needed.

Change the mixer speed to low and slowly add in the flour, baking soda, baking powder, cornstarch, salt and nutmeg. Mix in both of the oats and the chocolate chips and M&M's. Mixing until barely combined.

Remove the bowl from the mixer and use a standard sized cookie scoop (approximately 2 tablespoons) to scoop cookie dough balls. Option to roll the tops of the cookies in sprinkles before placing on the prepared cookie sheets.

Bake cookies, one cookie sheet at a time, in 350-degree oven for 11-12 minutes or until the edges of the cookies are light brown. Remove baked cookies from the oven and let rest on the cookie sheet for several minutes before transferring to a wire rack to finish cooling completely.