In a large mixing bowl, beat together the softened butter, creamy peanut butter, brown sugar, and granulated sugar until smooth, light, and fluffy, about 2–3 minutes. Use a hand mixer or a stand mixer with the paddle attachment.

Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract and scrape down the sides of the bowl so everything is evenly combined.

In a separate bowl, whisk together the rolled oats, all-purpose flour, baking soda, and fine sea salt until well combined.

Add the dry mixture to the peanut butter mixture. Mix on low speed just until most of the flour and oats are incorporated. The dough will be thick.

Gently fold in the chocolate chips, M&M’s, and peanut butter or butterscotch chips with a spatula or wooden spoon. Reserve a small handful of M&M’s to press on top of the dough balls before baking.

Cover the bowl and chill the dough in the refrigerator for at least 30 minutes and up to 24 hours. If chilling longer than 2 hours, let the dough sit at room temperature for 10–15 minutes before scooping.

When ready to bake, preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper or silicone baking mats.

Use a large cookie scoop (about 3 tablespoons of dough per cookie) to form dough balls and place them 3 inches apart on the prepared baking sheets. Gently press a few extra M&M’s on top of each dough ball for a colorful finish.

Bake one sheet at a time for 10–12 minutes, just until the edges are set and lightly golden and the centers still look slightly soft and puffy. They will continue to cook on the hot pan after you remove them from the oven.

Let the cookies cool on the baking sheet for 5–10 minutes, then transfer them to a wire rack to cool completely.