Name: Monster Cookie Bars Recipe
Prep time: 10 min
Cook time: 25 min
Total time: 35 min
Cuisine: American
Ingredients: 4 tablespoons (57 grams) unsalted butter, at cool room temperature; 3/4 cup (203 grams) natural peanut butter, very well stirred; 1/2 cup (100 grams) granulated sugar; 1/2 cup (100 grams) lightly packed dark brown sugar; 1 large egg plus 1 egg yolk, at cool room temperature; 1½ teaspoons vanilla extract; 2 cups (198 grams) old-fashioned rolled oats; 1 teaspoon baking soda; 1/4 teaspoon fine sea salt; 1/2 cup (85 grams) semisweet chocolate chips, plus extra for topping (optional); 1 cup (200 grams) M&M candies, plus extra for topping (optional); Flaky sea salt

Jump to Recipe· 4.4 from 88 reviews

If you have ever dreamed of a cookie that’s bursting with peanut butter goodness, loaded with chocolate chips and vibrant M&M candies, then this Monster Cookie Bars Recipe is your new best friend. Soft yet chewy, rich with peanut butter, and sprinkled with just the right amount of sweetness and crunch, these bars satisfy every craving and bring a party of textures and flavors right into your kitchen. They’re perfect for a crowd, snack time, or even a special treat to brighten your day. Trust me, once you make this Monster Cookie Bars Recipe, it will quickly become a staple you’ll want to bake again and again.

Ingredients You’ll Need

The image shows a close-up of a thick, square-shaped cookie bar with a rough texture. The bar has multiple layers: the base layer is dense and dark brown with visible oats mixed with small colorful candy pieces in blue, red, yellow, and orange. The top layer is similar but slightly crumbly with more candy pieces and oats. The cookie bar sits on a light brown parchment paper, with another similar bar blurred in the background. The surface beneath the parchment paper is a white marbled texture. photo taken with an iphone --ar 4:5 --v 7

The magic behind these bars comes from a handful of simple, well-chosen ingredients that each add a special touch. From the creamy peanut butter to the mix of oats and chocolate chips, every ingredient enhances the taste, texture, and color of this delightful dessert.

Unsalted butter: Adds richness and helps bind the bars together while keeping them moist.
Natural peanut butter: Provides that unmistakable nutty flavor and creamy texture; make sure it’s well stirred to mix evenly.
Granulated sugar: Brings sweetness and helps create a slightly crisp edge on the bars.
Dark brown sugar: Adds a deep, caramel-like sweetness and chewiness to the texture.
Egg and egg yolk: Act as binders to hold everything together and add richness.
Vanilla extract: Enhances the overall flavor with warm and sweet notes.
Old-fashioned rolled oats: Provide hearty chewiness and a wholesome element to the bars.
Baking soda: Helps the bars rise just enough and creates a tender crumb.
Fine sea salt: Balances the sweetness and brings out flavors.
Semisweet chocolate chips: Offer melty pockets of chocolate delight throughout the bars.
M&M candies: Add bursts of colorful crunch and fun to every bite.
Flaky sea salt (optional): A finishing touch that intensifies flavor and provides a lovely contrast.

How to Make Monster Cookie Bars Recipe

Step 1: Prepare Your Pan and Oven

Start by preheating your oven to 350°F and lining an 8×8-inch metal baking pan with foil or parchment paper. Don’t forget to spray it lightly with nonstick cooking spray to ensure easy removal later. This simple prep sets you up for perfect bars that come out cleanly and slice beautifully.

Step 2: Cream the Butters and Sugars

Using an electric mixer, beat the butter, natural peanut butter, granulated sugar, and brown sugar together on medium-high speed until the mixture becomes smooth and creamy, which usually takes about 2 to 3 minutes. Don’t rush this step; the creaminess here means better texture in your bars. Scrape down the bowl sides to mix everything evenly.

Step 3: Add Eggs and Vanilla

Next, beat in one large egg plus an extra egg yolk along with the vanilla extract until the batter is smooth again. These ingredients add richness and help bind your dough while lending that wonderful depth of flavor.

Step 4: Fold in the Dry Ingredients

Now mix in the oats, baking soda, and fine sea salt on low speed, just until they’re combined. Then gently fold in the semisweet chocolate chips and M&M candies with a rubber spatula, spreading them evenly throughout the dough without overmixing. The colorful candies make every bite exciting!

Step 5: Press Dough and Optional Chill

Firmly press the cookie dough evenly into your prepared pan using the back of a spatula or your hands. If you want bars with the best chew and flavor, cover the pan with plastic wrap and refrigerate the dough for 24 to 48 hours before baking. This step is a game-changer, but if you’re eager to bake right away, no worries — skip ahead happily.

Step 6: Bake to Perfection

Bake for 23 to 25 minutes, keeping an eye out for when the top looks set and lightly golden, and the center is no longer wet. Once out of the oven, place the pan on a wire rack and sprinkle flaky sea salt if you like that little extra flavor punch. Letting the bars cool completely is worth the wait — it helps the peanut butter flavor deepen and the texture firm up just right.

How to Serve Monster Cookie Bars Recipe

The image shows a batch of square oat bars with colorful candy pieces and chocolate chips mixed in, cut into 16 equal pieces and placed on white marbled surface. The oat bars have a rough, crumbly texture with visible oats and are light brown in color. Some candy pieces are bright red, green, yellow, orange, and blue, scattered across the bars and sticking out on top. Two pieces are separated from the main batch, showing the thickness and dense inside of the bars. Candy pieces also lie loose near the bars on the surface. Photo taken with an iphone --ar 4:5 --v 7

Garnishes

While these cookie bars are stunning on their own, adding a sprinkling of flaky sea salt right after baking highlights the sweet and salty contrast wonderfully. For a colorful finish, press a few extra M&Ms or chocolate chips on top before baking to create a festive, eye-catching look.

Side Dishes

Pair these bars with a tall glass of cold milk to balance out their sweetness and richness perfectly. For an indulgent snack, serve alongside a scoop of vanilla ice cream or a dollop of whipped cream to turn this treat into a dessert extravaganza.

Creative Ways to Present

Cut your Monster Cookie Bars Recipe into bite-sized squares and serve them on a beautiful platter for parties or family gatherings. You can also stack them with parchment sheets in between for grab-and-go treats or wrap individual bars in parchment paper tied with twine for thoughtful homemade gifts.

Make Ahead and Storage

Storing Leftovers

If you have any leftovers (and you might), store the Monster Cookie Bars in an airtight container at room temperature for up to 3 days. They maintain their chewy texture well but are best enjoyed fresh for maximum flavor and softness.

Freezing

You can freeze these bars either uncut or sliced into portions. Wrap them tightly in plastic wrap and place in a freezer-safe bag or container for up to 3 months. Thaw overnight in the fridge or at room temperature for a quick, delicious snack anytime.

Reheating

To revive that fresh-baked warmth, reheat your bars in the microwave for about 15 seconds, or pop them into a preheated 325°F oven for 5-7 minutes. This helps soften them up and brings back that freshly baked charm.

FAQs

Can I use crunchy peanut butter instead of natural peanut butter?

Absolutely! Crunchy peanut butter will add a nice texture and an extra nutty crunch to your bars, giving them a slightly different but just as delightful character.

What if I don’t have M&M candies? Are there alternatives?

If you don’t have M&Ms, you can substitute with any colorful coated chocolate candies you like, or just increase the amount of chocolate chips for a richer chocolate flavor.

Is it necessary to chill the dough before baking?

Chilling the dough is optional but highly recommended if you have the time. It deepens the flavor and improves the chewy texture, making your bars taste even more indulgent and satisfying.

Can these bars be made gluten-free?

Yes! Simply swap out the old-fashioned rolled oats for certified gluten-free oats to make this recipe safe for gluten-sensitive eaters without sacrificing texture or flavor.

How do I store Monster Cookie Bars in hot weather?

In warm climates, it’s best to store the bars in an airtight container in the refrigerator to prevent the chocolate from melting and the bars from becoming too soft.

Final Thoughts

There’s nothing quite like biting into a Monster Cookie Bars Recipe full of gooey peanut butter, melty chocolate, and colorful candy surprises. These bars are comfort food at its finest — easy to make, packed with flavor, and endlessly satisfying. I can’t wait for you to try this recipe and see how quickly it becomes a beloved treat in your home. Happy baking and even happier munching!