Chef Sarah Mitchell - Dessert Specialist
👨‍🍳 Dessert Chef

Recipe by Mitchell

🎓 Pastry Arts Graduate ⏰ 15+ Years Experience 🍽️ Cookie & Bar Expert

❤️ My Recipe Story

"These monster cookie bars were inspired by my childhood love of monster cookies, but simplified into an easy bar format. After testing dozens of variations, I found the perfect balance of chewy texture and loaded mix-ins."

Sarah specializes in approachable desserts that deliver maximum flavor with minimal fuss. She's perfected techniques for creating bakery-quality treats that home bakers can easily master in their own kitchens.

View All Mitchell's Recipes →
Golden-brown monster cookie bar squares with visible oats, chocolate chips, and colorful M&Ms, cut and arranged on a cooling rack

The Secret to Perfect Bar Texture

Achieving the ideal chewy texture in monster cookie bars requires careful attention to mixing and baking times. The combination of peanut butter and butter creates the perfect fat balance, while the oats provide structure and chewiness that sets these apart from regular cookie bars.

The key is not overbaking - the center should look just barely set when you remove them from the oven. They'll continue to cook slightly from residual heat, resulting in perfectly chewy bars that aren't dry or crumbly.

💡 Professional Tip

Press the dough firmly and evenly into the pan using slightly damp hands or the back of a measuring cup. This ensures even baking and clean cuts when slicing.

Frequently Asked Questions

Yes, crunchy peanut butter works well and adds extra texture. You might want to reduce or omit the chopped peanuts if using crunchy peanut butter to avoid too much crunch.

The edges should be set and lightly golden, while the center looks just barely set but not wet. They'll firm up as they cool. Don't overbake or they'll become dry.

Absolutely! Try chocolate candies, mini marshmallows, dried fruit, or additional chocolate chips. Keep the total amount of mix-ins about the same for best results.

Store covered at room temperature for up to 5 days, or freeze for up to 3 months. Layer between parchment paper if stacking to prevent sticking.

Yes, substitute the all-purpose flour with a 1:1 gluten-free flour blend. Make sure your oats are certified gluten-free as well.

This usually happens from underbaking or not pressing the dough firmly enough into the pan. Make sure edges are set before removing from oven.

Yes, double all ingredients and use a large sheet pan (18x13 inches). Baking time may increase slightly, so check for doneness around 30-32 minutes.

Cool completely, then use a sharp knife wiped clean between cuts. For extra clean lines, refrigerate the bars for 30 minutes before cutting.

Recipe Troubleshooting Guide

✅

Bars Too Dry

Problem: Cookie bars turn out dry and crumbly

Solution: Don't overbake - remove when center is just set. Check oven temperature accuracy and ensure proper measuring of wet ingredients.

✅

Bars Too Soft

Problem: Bars don't hold their shape when cut

Solution: Bake a few minutes longer until edges are golden. Allow to cool completely in the pan before cutting.

✅

Uneven Baking

Problem: Some areas bake faster than others

Prevention: Press dough evenly into corners and rotate pan halfway through baking. Check oven for hot spots.

✅

Mix-ins Sinking

Problem: Chocolate chips and M&Ms sink to bottom

Recovery: Lightly toss mix-ins in flour before folding into dough. Don't overmix once add-ins are incorporated.

✅

Sticking to Pan

Problem: Bars stick to the pan despite greasing

Prevention: Use parchment paper with overhang for easy removal. Let cool completely before attempting to remove.

✅

Flavor Balance Issues

Too Sweet: Add a pinch more salt or reduce sugar slightly

Too Salty: Increase vanilla extract or add more mix-ins

Bland: Increase vanilla, add cinnamon, or use more mix-ins for flavor interest

Ingredients for monster cookie bars including peanut butter, oats, chocolate chips, M&Ms, and baking ingredients arranged on a marble counter

Choosing Quality Ingredients

The foundation of exceptional monster cookie bars starts with quality peanut butter. Choose a creamy, well-stirred natural peanut butter or a reliable commercial brand. The peanut butter provides both flavor and structure, so its quality directly impacts the final result.

Old-fashioned oats are crucial for the signature chewy texture that defines monster cookies. Quick oats can be substituted but will create a less distinct texture. The oats absorb moisture during baking, contributing to the bars' satisfying chew.

Essential Ingredient Notes

  • Peanut Butter: Use creamy peanut butter that's well-mixed. Natural brands work great but make sure oil is fully incorporated before measuring.
  • Oats Selection: Old-fashioned rolled oats provide the best texture. Avoid instant oats which will break down too much during baking.
  • Mix-in Quality: Use fresh chocolate chips and M&Ms. Stale mix-ins can affect the overall taste and texture of your bars.
Monster cookie bar dough pressed into a parchment-lined baking pan, showing the loaded texture with visible oats, chocolate chips, and M&Ms

Mastering the Baking Process

Success with monster cookie bars lies in proper dough consistency and baking technique. The dough should be thick but spreadable, holding together well when pressed into the pan. If it seems too dry, the bars may crumble; too wet, and they won't hold their shape.

Baking at the right temperature and knowing when to stop is crucial. The bars continue cooking from residual heat after removal, so slightly underbaking ensures a chewy rather than crispy result. Look for set edges and a center that's firm but not hard.

The Perfect Press

Use slightly damp hands or the back of a measuring cup to press dough evenly into the pan. This creates uniform thickness for even baking and clean cuts.

Monster Cookie Bar Squares

Prep 15 min
Cook 28 min
Serves 24 servings
Level Easy

📋 Ingredients

Base Ingredients

  • 1 cup chocolate chips
    Use high-quality chips for best flavor
  • 1 cup M&M candies
    Regular size works best
  • 1/2 cup chopped peanuts
    Optional - adds extra crunch
  • Cooking spray
    For preparing the pan

Mix-ins and Add-ons

  • 1 cup creamy peanut butter
    Well-stirred for best consistency
  • 1/2 cup butter, softened
    Room temperature for easy mixing
  • 1 cup brown sugar, packed
    Adds moisture and molasses flavor
  • 1/2 cup granulated sugar
    Balances sweetness and texture
  • 3 large eggs
    Provides structure and richness
  • 2 tsp vanilla extract
    Enhances overall flavor
  • 1 1/2 cups old-fashioned oats
    Key for chewy texture
  • 1 cup all-purpose flour
    Provides structure

Instructions

  1. Prepare Pan and Oven

    Preheat oven to 350°F (175°C). Line a 9x13 inch baking pan with parchment paper and lightly spray with cooking spray.

  2. Mix Wet Ingredients

    In a large bowl, cream together peanut butter, butter, brown sugar, and granulated sugar until light and fluffy, about 3-4 minutes. Beat in eggs one at a time, then vanilla extract.

  3. Combine Dry Ingredients

    In a separate bowl, whisk together oats, flour, baking soda, and salt. Gradually mix dry ingredients into wet ingredients until just combined.

  4. Add Mix-ins

    Fold in chocolate chips, M&Ms, and peanuts (if using) until evenly distributed throughout the dough.

  5. Bake and Cool

    Press dough evenly into prepared pan. Bake for 25-28 minutes until edges are set and center is just barely set. Cool completely in pan before cutting into squares.

Recipe Notes & Tips

Storage

Store bars covered at room temperature for up to 5 days. For longer storage, wrap individually and freeze for up to 3 months.

Serving Suggestions

Serve at room temperature for best texture. These are perfect for lunch boxes, potlucks, or as an after-school snack with a glass of milk.

Variations

Try different mix-ins like white chocolate chips, butterscotch chips, dried fruit, or coconut flakes. You can also add a teaspoon of cinnamon to the dry ingredients for extra warmth.