Dessert

Monster Cookie Bars Recipe

ByElla Hart November 6, 2025November 6, 2025

Introduction

Monster Cookie Bars are a delightful treat combining the rich flavors of peanut butter, oats, and chocolate chips with colorful m&m’s for an irresistible, chewy texture. Perfect for snacking or sharing, these bars bring the classic cookie experience in an easy-to-cut square form.

The image shows close-up squares of a layered dessert bar, each piece having a crumbly, golden brown top layer with a rough texture. Below the top are scattered colorful candy-coated chocolate pieces in red, green, yellow, orange, and blue, mixed with chunks of melted chocolate chips that create a glossy, rich dark brown layer underneath. The bottom layer appears to be a firm but chewy base of baked crust with a light brown color. The bars rest on a white marbled surface, with visible flaky salt crystals sprinkled on top adding texture contrast. photo taken with an iphone --ar 4:5 --v 7

Ingredients

1/2 cup (111g) salted butter, softened
1/4 cup (62g) peanut butter
1 cup (246g) brown sugar
1/4 cup (58g) granulated sugar
2 eggs
2 tsp vanilla extract
2 cups (304g) all-purpose flour
1 cup (100g) rolled oats
1 tsp baking soda
1/2 tsp baking powder
1/2 tsp salt
1 cup (200g) semi sweet chocolate chips
3/4 cup (150g) m&m’s

Instructions

Step 1: Line a 9×9 inch pan with parchment paper and set aside.
Step 2: Preheat your oven to 350°F (180°C).
Step 3: In a large bowl, cream together the softened butter, peanut butter, brown sugar, and granulated sugar until smooth and creamy.
Step 4: Add the eggs and vanilla extract, mixing until well combined.
Step 5: In a separate bowl, whisk together the flour, rolled oats, baking soda, baking powder, and salt. Gradually add this to the wet ingredients and mix until a sticky dough forms.
Step 6: Fold in the chocolate chips and m&m’s evenly throughout the dough.
Step 7: Pour the dough into the prepared pan and press it down loosely but firmly to create an even layer.
Step 8: Bake in the preheated oven for 25 to 30 minutes, or until the tops are golden brown.
Step 9: Remove the pan from the oven and allow the cookie bars to cool completely before lifting them out and cutting into squares.
Step 10: Enjoy your delicious Monster Cookie Bars!

Tips & Variations

For extra chewiness, use old-fashioned rolled oats instead of quick oats.
Try swapping m&m’s for peanut butter chips or butterscotch chips for a different flavor.
Chill the dough in the pan for 15 minutes before baking to help the bars hold their shape better.
Use natural peanut butter for a less sweet, more authentic peanut flavor.

Storage

Store the cookie bars in an airtight container at room temperature for up to 3-4 days. To keep them fresh longer, you can refrigerate for up to a week or freeze for up to 3 months. When reheating, warm briefly in the microwave or oven to restore softness and flavor.

How to Serve

The image shows thick square bars with three visible layers: the bottom layer is a dense brown chocolate base, the middle layer is rich melted chocolate with chocolate chips, and the top layer is crumbly and golden brown cookie dough dotted with colorful candy coated chocolates in red, green, blue, yellow, and orange. Some chocolate chips peek through the crumbled top layer, and there are small flakes of coarse salt sprinkled on top. The bars rest closely together on a white marbled surface. photo taken with an iphone --ar 4:5 --v 7

Serve this delicious recipe with your favorite sides.

FAQs

Can I use crunchy peanut butter instead of smooth?

Yes, crunchy peanut butter will add a pleasant texture to the bars but may change the smoothness of the dough slightly.

Do I need to use parchment paper to line the pan?

Parchment paper makes it much easier to remove the bars from the pan cleanly and helps prevent sticking. If you don’t have it, lightly grease the pan instead.