Place butter, sugars, eggs, vanilla, and peanut butter in a large bowl.
Using a hand mixer or stand mixer, beat together until well combined.
Add in oats, baking soda, salt, M&Ms, and chocolate chips.
Mix until well combined.
Optional: chill the dough for at least 30 minutes. I never do this, but if you're worried about spreading, I'd recommend chilling the dough.
Preheat oven to 350 degrees F and line a rimmed baking sheet with a silicone baking mat.
Use a cookie scoop** to scoop cookie onto prepared baking sheet. I bake 12 at a time.
Depending on the size of your cookie scoop, bake cookies for 8-12 minutes (8 for smaller cookies, 12 for larger cookies).
Remove from oven and let cool for a few minutes, before removing them from the cookie sheet and placing the cookies on a cooling rack.
Serve immediately or cool completely before storing in airtight containers!
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