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Monster Cookie Bars
5 from 2 votes

Monster Cookie Bars

Monster Cookie Bars are gooey, chewy, and ultra-thick, packed with peanut butter flavor, and loaded with chocolate chips and M&Ms. These cookie bars are easy to make, ready in under 45 minutes!

Prep Time
20 mins
Cook Time
23 mins
Total Time
43 mins
Servings: 16 cookie
Course: Dessert
Cuisine: American

Ingredients

  • 4 tablespoons unsalted butter at cool room temperature, 57 grams
  • 3/4 cup natural peanut butter very well stirred, 203 grams
  • 1/2 cup granulated sugar 100 grams
  • 1/2 cup dark brown sugar lightly packed (100 grams
  • 1 egg at cool room temperature, large plus 1 yolk
  • 1½ teaspoons vanilla extract
  • 2 cups old-fashioned rolled oats 198 grams
  • 1 teaspoon baking soda
  • 1/4 teaspoon salt
  • 1/2 cup semisweet chocolate chips plus extras to top cookie bars, optional, 85 grams
  • 1 cup M&M candies plus extras to top cookie bars, optional, 200 grams
  • sea salt for topping, optional, flaky

Instructions

    Cup of Yum
  1. Preheat the oven to 350°F. Line an 8 by 8-inch metal baking pan with foil or parchment paper. Spray with nonstick cooking spray.
  2. In the bowl of an electric mixer, beat the butter, peanut butter, granulated sugar, and brown sugar on medium-high speed until smooth and creamy, 2 to 3 minutes. Scrape down the bottom and sides of bowl. Beat in the egg, egg yolk, and vanilla. Add the oats, baking soda, and salt, mixing on low speed until combined. Fold in the chocolate chips and M&Ms with a rubber spatula.
  3. Press dough evenly into prepared pan. Optional: Dot the tops of the bars with additional M&Ms and/or chocolate chips before baking.
  4. If time permits, cover pan with plastic wrap and refrigerate for 24-48 hours to yield a chewier, more flavorful bar.
  5. Bake for about 23-25 minutes, or until the bars no longer look wet on top, the center appears set, and the top is golden brown. Set pan on a wire rack and sprinkle flaky sea salt on top, if desired. For best texture and to allow the peanut butter flavor to fully develop, let bars sit until completely cooled before slicing and enjoying. It’s worth it, promise!
  6. Cookie bars can be stored in an airtight container at room temperature for up to 3 days.

Notes

  • *We recommend using natural peanut butter that’s been very well stirred as it will yield a much bolder peanut butter flavor; however, conventional peanut butter (Skippy and Jif) work well too. You can alternatively use almond butter at a 1:1 ratio.
  • **Using dark brown sugar will yield a chewier, richer cookie bar but may be substituted at a 1:1 ratio with light brown sugar.
  • Please note that this recipe does not require any flour, making these cookie bars a great gluten-free option (if using certified gluten-free ingredients).