01 -
Preheat the oven to 350°F. Line large rimmed baking sheets with parchment paper and set aside.
02 -
In a medium bowl, whisk together the all-purpose flour, rolled oats, baking powder, baking soda, and Kosher salt until well combined. Set aside.
03 -
Using a stand mixer fitted with the paddle attachment, beat the softened butter, light brown sugar, and granulated sugar on medium speed until creamy and thoroughly combined, about 2 minutes. Scrape down the bowl as needed.
04 -
Add the vanilla extract, egg, and creamy peanut butter to the creamed mixture and mix until smooth, about 1 minute.
05 -
Reduce mixer speed to low and gradually add the dry ingredient mixture. Mix until just combined and no visible streaks of flour remain.
06 -
Gently stir in the chopped bittersweet chocolate, 1/4 cup of the M&Ms, and semisweet chocolate chips until evenly distributed.
07 -
Scoop and shape the dough into 2 tablespoon-sized balls, about 55 grams each, arranging them evenly on prepared baking sheets spaced 2 inches apart.
08 -
Bake in batches for 10 to 12 minutes, or until the edges are golden and the centers appear mostly set.
09 -
Remove trays from oven and immediately top each cookie with additional M&Ms, pressing gently into the surface.
10 -
Let cookies rest on the baking sheet for 5 to 10 minutes before transferring to a wire rack to cool completely. The cookies will continue to set as they cool.