Name: Monster Cookie Bars
Prep time: 15 min
Cook time: 30 min
Total time: 1 h 15 min
Cuisine: American
Ingredients: 1 1/2 cups old-fashioned oats; 1 cup all-purpose flour; 1/2 teaspoon baking soda; 1/2 teaspoon salt; 1/2 cup (1 stick) unsalted butter, softened; 3/4 cup brown sugar; 1/4 cup granulated sugar; 2 large eggs; 3/4 cup creamy peanut butter; 1 teaspoon vanilla extract; 1 cup semi-sweet chocolate chips; 1 cup candy-coated chocolates (such as M&M’s), divided

Why You’ll Love This Recipe

Monster Cookie Bars are packed with flavor and texture—sweet, salty, soft, and just the right amount of crunchy. They’re easy to customize with your favorite mix-ins and bake up in one pan, saving you the time and effort of scooping individual cookies. Plus, they hold up well for storing and travel, making them ideal for sharing or batch baking.

Ingredients

(Tip: You’ll find the full list of ingredients and measurements in the recipe card below.)

Old-fashioned oats
All-purpose flour
Baking soda
Salt
Unsalted butter (softened)
Brown sugar
Granulated sugar
Eggs
Creamy peanut butter
Vanilla extract
Semi-sweet chocolate chips
Candy-coated chocolates (such as M&M’s)

Directions

Preheat your oven to 350°F (175°C). Grease or line a 9×13-inch baking pan with parchment paper.
In a bowl, whisk together oats, flour, baking soda, and salt. Set aside.
In a large mixing bowl, cream together the butter, brown sugar, and granulated sugar until light and fluffy.
Beat in the eggs one at a time, followed by the peanut butter and vanilla extract.
Gradually add the dry ingredients to the wet ingredients, mixing until fully incorporated.
Stir in the chocolate chips and candy-coated chocolates, reserving a handful for topping.
Spread the dough evenly in the prepared pan. Press the reserved candies lightly on top.
Bake for 25–30 minutes, or until the edges are golden and the center is just set.
Cool completely in the pan before slicing into bars.

Servings and timing

This recipe yields approximately 20 bars.
Prep time: 15 minutes
Bake time: 25–30 minutes
Cooling time: 30 minutes
Total time: About 1 hour and 15 minutes

Variations

Use quick oats for a slightly softer texture.
Swap peanut butter for almond butter or sunflower seed butter for allergy-friendly versions.
Add chopped nuts, mini marshmallows, or toffee bits for extra variety.
Use holiday-themed M&M’s for festive occasions.
Stir in white chocolate or butterscotch chips for a flavor twist.

Storage/Reheating

Store Monster Cookie Bars in an airtight container at room temperature for up to 5 days.
Refrigerate for a firmer texture or freeze for up to 2 months.
To serve warm, microwave a bar for 10–15 seconds.

FAQs

Can I use natural peanut butter?

You can, but for best results, use a no-stir variety to avoid excess oil and separation.

Do I have to chill the dough?

No chilling is needed for this recipe. It’s designed for quick mixing and baking.

Can I use quick oats instead of old-fashioned?

Yes, quick oats will work, though the texture will be slightly less chewy.

Can I double the recipe?

Absolutely. Use a half-sheet pan and increase baking time slightly, watching for doneness.

Are these bars gluten-free?

They can be if you use certified gluten-free oats and a 1:1 gluten-free flour blend.

What kind of candy works best?

Classic M&M’s are traditional, but you can use peanut butter, caramel, or mini versions for variety.

How do I know when they’re done baking?

The edges should be golden, and the center should look just set—do not overbake for best texture.

Can I skip the chocolate chips?

Yes, but the chocolate adds richness. Feel free to reduce or substitute with nuts or dried fruit.

Can I make them without peanut butter?

Yes, but they’ll lose some of their signature flavor. Substitute with another nut or seed butter.

What’s the best way to cut clean bars?

Cool completely, then use a sharp knife. For cleaner edges, chill before slicing.

Conclusion

Monster Cookie Bars are the ultimate treat for when you want big cookie flavor without the hassle. Loaded with oats, peanut butter, chocolate, and colorful candies, they’re fun, filling, and easy to bake in one pan. Whether you’re making them for a celebration or stashing some for later, these bars are guaranteed to hit the sweet spot.