Preheat your oven to 350°F. Line baking sheets with parchment paper—these cookies can get a little sticky on the bottom without it!
In a large mixing bowl (you'll need a big one for this recipe!), beat together the peanut butter, brown sugar, granulated sugar, and butter until creamy and well combined, about 2 minutes.
Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.
In a separate bowl, stir together the oats, baking soda, and salt. Add this to the peanut butter mixture and mix until well combined.
Fold in the chocolate chips and M&Ms, reserving a handful of each to press into the tops of the cookies before baking (this makes them extra pretty!).
Scoop the dough using a 2-tablespoon cookie scoop or roll into golf ball-sized portions. Place them 3 inches apart on your prepared baking sheets—they spread quite a bit.
Gently press a few extra chocolate chips and M&Ms into the top of each cookie dough ball for that bakery-style look.
Bake for 13-15 minutes, until the edges are golden brown but the centers still look slightly underdone. They'll continue to cook on the pan!
Let cookies cool on the baking sheet for 5 minutes before transferring to a wire rack. These are best enjoyed while still slightly warm, when all the chocolate is melty!
