Instructions

• Fit a stand mixer with the paddle attachment or use a large bowl and a handheld electric mixer. In the mixing bowl, beat the room-temperature butter on medium speed until smooth and creamy, about 1–2 minutes.
• Add the room-temperature peanut butter and vanilla extract. Beat on medium until fully combined and smooth, about 1–2 minutes, scraping down the sides and bottom of the bowl as needed.
• Add the light brown sugar and granulated sugar. Beat on medium-high until the mixture is light and fluffy, about 2 minutes, stopping once or twice to scrape down the bowl.
• Add the eggs and the egg yolk one at a time, beating well after each addition until incorporated. Turn the mixer off.
• In a separate medium bowl, whisk together the all-purpose flour, old-fashioned oats, quick oats, baking soda, baking powder, ground cinnamon, and salt until evenly combined.
• With the mixer on low, add the dry mixture to the wet ingredients and mix just until no streaks of flour remain. Do not overmix.
• Turn the mixer off and use a rubber spatula to fold in the M&M candies, semi-sweet chocolate chips, and roughly chopped salted peanuts until evenly distributed.
• Cover the bowl and refrigerate the dough for at least 30 minutes (this firms the dough and helps control spreading). You may chill the dough up to 2 days; if chilling longer than 30 minutes, bring it back to slightly softened but still cold before scooping.
• When ready to bake, preheat the oven to 350°F and position a rack in the middle. Line two large baking sheets with parchment paper.
• Using a cookie scoop or tablespoons, portion the dough into 2-tablespoon mounds and place them on the prepared sheets, leaving 2–3 inches between each mound for spreading. Gently press each mound slightly to flatten the top. If desired, sprinkle a few extra oats on top of each cookie.
• Bake one tray at a time on the middle rack for about 12 minutes, or until the edges are golden and the centers are set. If you prefer a softer center, check a minute or two earlier.
• Remove the baking sheet from the oven. If any cookie edges have spread unevenly, gently press them back toward the center with a spatula while still warm.
• Let the cookies cool on the baking sheet for 10 minutes, then transfer them to a cooling rack to cool completely.