Cookie Bars: Soft and Chewy Monster Cookie Bars in One Pan

Cookie Bars are the kind of dessert that solve everything at once. You get the nostalgic flavor of classic cookies, the ease of baking everything in a single pan, and slices that stay soft for days. These Monster Cookie Bars bring together peanut butter, hearty oats, chocolate chips, and colorful M&M’s for a dessert that feels familiar yet special. Whether you need an easy treat for a gathering or a dependable bake-once dessert for the week, this recipe delivers big flavor with minimal effort.

I started making Cookie Bars when I wanted all the comfort of cookies without the extra work of scooping dough and baking batch after batch. Over time, these Monster Cookie Bars became a favorite because they combine everything people love in one pan. Cookie Bars like these feel generous and relaxed, perfect for sharing. The peanut butter adds richness, the oats give structure, and the candy brings color and crunch. When I need a dessert that always works, I reach for these Cookie Bars because they bake evenly, slice cleanly, and taste even better the next day.

Ingredients

• 2 cups all-purpose flour, spooned and leveled

• 2 cups old fashioned oats

• 1 teaspoon baking soda

• 1 teaspoon sea salt

• 1 cup unsalted butter, at room temperature

• 1 cup creamy peanut butter

• 1 1/2 cups packed light brown sugar

• 1/2 cup granulated sugar

• 2 large eggs

• 1 tablespoon vanilla extract

• 1 1/4 cups semi-sweet chocolate chips

• 1 1/2 cups M&M’s, divided

• Flaky sea salt, for sprinkling

Step-by-Step Instructions

Preparing the Ingredients

Start by preheating your oven to 350 degrees F and greasing a 9×13-inch pan generously with nonstick spray. Measure the flour carefully and level it for accuracy, then combine it with the oats, baking soda, and salt in a bowl. Let the butter come fully to room temperature so it blends smoothly with the peanut butter and sugars, which helps create soft Cookie Bars with an even crumb.

Cooking Instructions

Cream the butter, peanut butter, and both sugars together until smooth and fluffy, then mix in the eggs and vanilla until fully combined. Add the dry ingredients and mix just until the dough comes together, then fold in the chocolate chips and most of the M&M’s. Spread the dough evenly into the prepared pan, press the remaining M&M’s on top, and bake until lightly golden and set. Finish with a sprinkle of flaky salt and allow the bars to cool completely before slicing.

Tips for Perfect Results

Common Mistakes to Avoid

Overbaking is the quickest way to dry out Cookie Bars, so watch closely toward the end of baking time. Mixing the dough too much after adding the flour can make the bars dense instead of chewy. Skipping proper pan greasing may cause sticking, which leads to uneven slices and broken edges when serving.

Pro Tips for Better Flavor

Use creamy peanut butter rather than natural styles for consistent texture. Chilling the dough briefly can deepen flavor and slightly soften the oats. Pressing extra candy on top before baking keeps the bars colorful and makes them look bakery ready once sliced.

Serving and Storage

How to Serve

Slice these bars into neat squares and serve them at room temperature for the best texture. They work well for parties, bake sales, or casual desserts, and they pair nicely with milk or coffee. Because they are sturdy, they also travel well for potlucks or holiday trays, including spring gatherings and easter treats.

How to Store Leftovers

Store leftover Cookie Bars in an airtight container at room temperature for up to four days. For longer storage, refrigerate them to maintain freshness and chewiness. You can also freeze individual bars tightly wrapped, then thaw at room temperature when ready to enjoy.

Conclusion

These Monster Cookie Bars prove that simple ingredients and one pan can still create a memorable dessert. With their soft centers, chewy edges, and colorful topping, they fit almost any occasion. Bake a pan once, slice, and share, and you will have a reliable recipe that people ask for again and again.

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Frequently Asked Questions

Can I make these Cookie Bars ahead of time?

Yes, you can prepare the dough up to forty-eight hours in advance and keep it chilled. This resting time allows the oats to soften and the flavors to blend, which results in bars that bake evenly and taste even richer once cooked.

What makes these Monster Cookie Bars different from cookies?

Unlike traditional cookies, these bars bake all at once in a pan, which creates a mix of textures from edge to center. They also hold moisture longer, making them softer over several days compared to individual cookies.

Can I customize the mix-ins?

You can swap the M&M’s for other candy-coated chocolates or add chopped nuts if desired. The base works well for monster cookies, peanut butter oatmeal bars, or m&m dessert bars, as long as the total mix-in amount stays similar.

Cookie Bars

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• Author: Emily Carter
• Total Time: 40 minutes
• Yield: 24 bars 1x
• Diet: Vegetarian

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Description

Soft and chewy Monster Cookie Bars made with peanut butter, oats, chocolate chips, and colorful M&M’s baked in one pan.

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Ingredients

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• 2 cups all-purpose flour
• 2 cups old fashioned oats
• 1 teaspoon baking soda
• 1 teaspoon sea salt
• 1 cup unsalted butter, room temperature
• 1 cup creamy peanut butter
• 1 1/2 cups light brown sugar
• 1/2 cup granulated sugar
• 2 large eggs
• 1 tablespoon vanilla extract
• 1 1/4 cups semi-sweet chocolate chips
• 1 1/2 cups M&M’s
• Flaky sea salt

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Instructions

1. Preheat oven to 350 degrees F and grease a 9×13-inch pan.
2. Whisk together flour, oats, baking soda, and salt.
3. Cream butter, peanut butter, and sugars until smooth.
4. Add eggs and vanilla and mix until combined.
5. Mix in dry ingredients just until combined.
6. Stir in chocolate chips and 1 cup of M&M’s.
7. Spread dough evenly into prepared pan.
8. Top with remaining M&M’s.
9. Bake 25–35 minutes until lightly golden and set.
10. Sprinkle with flaky sea salt and cool before slicing.

Notes

1. Do not overbake to keep bars soft.
2. Dough can be chilled up to 48 hours before baking.

• Prep Time: 10 minutes
• Cook Time: 30 minutes
• Category: Dessert
• Method: Baking
• Cuisine: American

Nutrition

• Serving Size: 1 bar
• Calories: 320
• Sugar: 26g
• Sodium: 210mg
• Fat: 18g
• Saturated Fat: 9g
• Unsaturated Fat: 8g
• Trans Fat: 0g
• Carbohydrates: 36g
• Fiber: 3g
• Protein: 6g
• Cholesterol: 55mg