Monster Cookies are thick and chewy, loaded with peanut butter, oats, chocolate chips, and M&Ms. They've got all the good stuff wrapped up in one cookie and are great for making ahead of time!
In the bowl of a stand mixer, or in a large bowl with an electric mixer, combine peanut butter, butter, granulated sugar and brown sugar until smooth. Beat in the egg and vanilla until combined.
Add the oats, flour, baking soda, and salt and mix until just combined. Stir in M&Ms and chocolate chips with a spatula or wooden spoon.
Line 2 baking sheets with parchment paper. Roll or scoop cookie dough into 1½" balls (about 2 tablespoons) and place 2" apart on the baking sheet (I do 12 to one baking sheet). Bake for 9-10 minutes until just slightly glossy in the center and golden at the edges. Remove from the oven and let cool for 10 minutes before removing to a cooling rack.
If desired, press additional M&Ms into the tops of the cookies while they're fresh from the oven.
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Notes
Cookie size: I've made these both smaller (with a 1.5 tablespoon scoop) and larger (with an ice cream scoop) -- both work just as well, you you will get 3 dozen or 1 dozen respectively. Just remember to adjust the bake time as needed!Storage: these cookies can be stored at room temperature for several days or frozen up to 3 months.To make ahead: you can scoop and freeze cookie dough balls, then store in an airtight freezer bag. Bake from frozen, adding 1-2 minutes to the bake time as needed.