Ingredients

• 1½ cups all-purpose flour
• 1 cup quick oats
• ¾ teaspoon baking soda
• ¼ teaspoon salt
• 1/2 cup butter (softened)
• 1/3 cup creamy peanut butter (not all natural)
• 1/2 cup granulated sugar
• 1/2 cup packed light brown sugar
• 1 teaspoon vanilla extract
• 1 large egg
• 1 large egg yolk (discard the whites, only use the yolk)
• 1/2 cup peanut butter chips
• 1/2 cup miniature semi-sweet chocolate chips
• 1/2 cup mini m&m's

Steps

1. Preheat the oven to 350℉. Lightly spray a 9x13-inch baking pan with cooking spray or line with parchment paper.*I prefer using parchment paper because then you can lift the bars out for even cutting and slicing.
2. In a small mixing bowl, whisk together the all-purpose flour, quick oats, baking soda, and salt. Set aside.
3. In a separate larger bowl using a hand mixer, or use a stand mixer with the paddle attachment, beat together the butter, peanut butter, sugar, and brown sugar until it's fluffy, combined well, and much lighter in color; about 2 minutes of beating on medium speed.
4. Add in the vanilla extract, egg, and egg yolk. Beat just until combined.
5. Add the dry ingredients, peanut butter chips, mini chocolate chips, and mini m&m's into the larger bowl of wet ingredients. Beat on low speed just until combined well.
6. Dump the monster cookie bar dough into the prepared pan and gently press it into the pan in an even layer; don't pack it too firmly into the pan, use a gently hand to spread it out evenly. *If wanted, add a few extra mini m&m's and mini chocolate chips on top of the bars for a pretty look.
7. Bake for 12-16 minutes. The bars should be very lightly pale brown on the edges, while the center should still be pale and look slightly underdone.*It's important to not over-bake the bars because as they cool in the warm pan, they will continue baking and set up perfectly soft.
8. Let the bars cool, inside the warm pan at room temperature, for about 20 minutes. Cut into squares and enjoy warm or at room temperature.