Inspired by monster cookies, these monster cookie bars are chewy peanut butter oatmeal bars packed with M&M candies and chocolate chips. They're made in one bowl and baked in under an hour!
Line a 9x13 baking pan with parchment paper or grease the sides and bottom with nonstick spray or butter. Then preheat the oven to 350 F/180 C.
In a mixing bowl, cream the butter, peanut butter, brown sugar, and granulated sugar until light and fluffy.
Mix in the eggs, egg yolks, and vanilla.
Fold in the flour, oats, baking soda, salt, chocolate chips, chopped chocolate, and M&Ms until just combined. Do not overmix! Evenly spread the cookie dough into the prepared baking pan. Sprinkle the top with extra chocolate chips, chopped chocolate, and M&Ms if desired.
Bake in the preheated oven for 25-35 minutes or until the top is golden brown and a toothpick inserted into the center comes out just barely moist. Let them cool completely on a wire rack before cutting then enjoy!
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Notes
*Measure your flour properly. This is my #1 baking tip! Do not ever scoop a measuring cup into your flour as this always leads to using too much flour. Instead, use the spoon-level method. This means fluffing the flour first, then spooning it into your measuring cup/spoon. For the BEST results, use a kitchen scale!*