4 1/2 cups (18 ounces) quick cooking oats (double check oats are gluten-free if making gluten-free cookies)
1 cup (8 ounces) M&Ms
1 cup (6 ounces) milk chocolate, semisweet, or bittersweet chocolate chips
Preheat the oven to 350 degrees F. Line cookie sheets with parchment paper, silpat liners or lightly grease with cooking spray.
In a large mixing bowl with a handheld electric mixer (or in a stand mixer fitted with the paddle attachment), add the eggs, brown sugar, and granulated sugar. Mix well.
Add the salt, baking soda, vanilla, peanut butter and butter. Mix until creamy and well combined, 1-2 minutes.
Stir in the oatmeal, M&Ms, and chocolate chips until combined. The dough will be sticky.
Scoop the dough into heaping tablespoon-sized balls (see note above) and place about 2 inches apart on the cookie sheets. If you want the cookies thinner, flatten them slightly with the palm of your hand.
Bake the cookies for 8-10 minutes. Don’t overbake – the cookies should just be set and very lightly golden around the edges.
Let the cookies sit for 1-2 minutes on the cookie sheet before transferring to a cooling rack to cool completely. Store in a airtight container for 2 days (the baked cookies freeze well, also).
Keep in mind that if you want the cookies to be safely gluten-free, make sure your oats are certified gluten-free (it will say on the package if they are). Speaking of oats, several commenters have successfully used old-fashioned oats (the cookies may spread a bit more). Or you could take your old-fashioned oats and process them lightly in a blender before using (measure after they have been blended a bit).
Also, lots of times when I make these, I sub in different kinds of chips. Peanut butter chips are dreamy (in addition to or in place of M&Ms or part of the chocolate chips). Finally, many of you commented you’ve gotten a lot more than 2-3 dozen cookies out of this batch and that’s because you make your cookies small and I make mine not-small. Sometimes, I use my #40 medium cookie scoop which is about 1 1/2 to 2 tablespoons but a lot of time, I grab the #20 scoop which is 3 tablespoons or more. I mean, we’re going for monster cookie here, right?