Monster Cookie Bars
If you're looking for the ultimate feel-good, crowd-pleasing dessert, these Monster Cookie Bars check all the boxes. They’re chewy, chocolatey, a little salty-sweet, and packed with colorful fun thanks to the M&Ms.
Why I love monster cookies: they include all of my favorite sweet tooth cravings. Chocolate, peanut butter, butterscotch, and oatmeal and require no need to chill dough or scoop individual cookies. I created these bars to capture that peanut-buttery goodness in a no-fuss, one-pan version. They’re easier to make than cookies, but just as addictive.
Ingredients
| Ingredient | Amount | Purpose |
|---|---|---|
| Salted Butter (melted) | ½ cup | Adds richness and moisture. Melting helps give a fudgy, chewy texture. Salted butter also balances sweetness. |
| Brown Sugar | 1 cup | Adds sweetness and moisture. Brown sugar helps the bars stay soft and adds a caramel-like flavor. |
| Eggs (room temp) | 2 large | Provide structure and help the bars hold together. Room temp eggs mix more evenly. |
| Vanilla Extract | 1 tbsp | Enhances flavor and adds warmth. |
| Creamy Peanut Butter | ¼ cup | Adds flavor, richness, and a soft texture. Also complements the chocolate beautifully. |
| All-Purpose Flour | 1 cup | The main structure of the bars. |
| Baking Powder | ½ tsp | Helps the bars rise slightly and not turn out too dense. |
| Salt | ½ tsp | Enhances all the other flavors and balances sweetness. |
| Rolled Oats | ½ cup | Add chewiness and a bit of texture. Classic in monster cookies. |
| M&Ms | ¾ cup (+ extra for top) | Add color, crunch, and pockets of chocolate. Topping makes them look extra fun. |
| Chocolate Chips | ½ cup | Melty chocolate throughout for gooey bites. |
| Butterscotch Chips | ½ cup | Sweet and buttery flavor that complements the peanut butter and oats. |
Step-by-Step Instructions
Step 1: Prep Your Pan & Oven
Preheat your oven to 350°F (175°C).
Line a 9x9-inch baking pan with parchment paper, leaving some overhang so you can easily lift the bars out later. This prevents sticking and helps with easy cleanup.
Tip: Lightly grease the pan before adding parchment so it stays in place.
Step 2: Melt the Butter
Melt ½ cup of salted butter in a microwave-safe bowl or on the stovetop.
Let it cool slightly (about 5 minutes). You want it warm, not hot, so it doesn’t cook the eggs.
Why melt it? Melted butter creates a denser, chewier texture, perfect for bars.
Step 3: Mix Wet Ingredients
In a large mixing bowl, add the melted butter and 1 cup brown sugar. Stir with a spatula or wooden spoon until combined and smooth.
Add 2 room-temperature eggs and 1 tablespoon of vanilla extract. Mix until just combined.
Add ¼ cup creamy peanut butter and stir until fully incorporated.
Tip: Use room temp eggs to help everything mix evenly and prevent curdling.
Step 4: Add Dry Ingredients
Sprinkle in 1 cup of flour, ½ tsp baking powder, and ½ tsp salt.
Gently fold the mixture together using a spatula. Mix just until you no longer see dry flour; don’t overmix.
Why fold? Overmixing can make the bars tough. Gentle folding keeps them soft and chewy.
Step 5: Add the Fun Stuff!
Fold in:
¾ cup M&Ms
½ cup chocolate chips
½ cup butterscotch chips
½ cup rolled oats
Tip: Save a few M&Ms to press on top of the dough just before baking. It makes the bars look bakery-style!
Step 6: Bake
Pour the batter into your prepared pan and spread it evenly.
Bake for 30–35 minutes, or until:
The edges are golden brown.
The center looks set but slightly soft (it will firm up as it cools).
Don't overbake! Slightly underbaking = gooey, soft bars. A toothpick inserted in the center should come out with a few moist crumbs (not raw batter).
Step 7: Cool & Slice
When the bars are out of the oven. Carefully press a few extra M&Ms, chocolate chips, and butterscotch chips on top for decoration.
Let the bars cool completely in the pan. This helps them set and makes slicing easier.
Once cool, lift them out using the parchment paper and slice into squares.
Ingredient Swaps & Variations
| Ingredient | Swap Option | Notes |
|---|---|---|
| Salted Butter | Unsalted Butter + ¼ tsp extra salt | Balances flavor if using unsalted butter. |
| Peanut Butter | Almond Butter or Sunflower Seed Butter | Great for peanut allergies. Use creamy, not natural oils-on-top types. |
| M&Ms | Mini M&Ms, Reese’s Pieces, or Chopped Candy | For fun variations or seasonal themes. Reese’s adds more peanut butter flavor. |
| Butterscotch Chips | White Chocolate Chips or Extra Chocolate Chips | Use based on your taste preferences or what you have on hand. |
| Rolled Oats | Quick Oats | Softer texture. Avoid steel-cut oats—they’re too coarse for baking. |
| Brown Sugar | Coconut Sugar | Less sweet with a deeper, molasses-like flavor. Good for a natural option. |
Extra Tips for Success
Don’t skip the parchment paper – it makes removing the bars clean and easy.
Use room-temperature ingredients – eggs and peanut butter mix better when not cold.
Customize mix-ins – Add chopped nuts, shredded coconut, or a swirl of Nutella!
Double the recipe – for a crowd, double the ingredients and use a 9x13 pan. Add 5–10 minutes to the bake time.
How to Store Monster Cookie Bars
Room Temperature
Storage Time: Up to 5 days
How: Place the cooled bars in an airtight container, separating layers with parchment or wax paper to prevent sticking.
Tip: Store in a cool, dry place away from direct sunlight or heat sources.
Best for keeping the bars soft and chewy without any extra steps.
Refrigerator
Storage Time: Up to 1 week
How: Use an airtight container or tightly wrap the entire slab in plastic wrap.
Tip: Let bars sit at room temp for 10–15 minutes before serving to soften slightly, or warm briefly in the microwave.
Chilling helps extend shelf life but may make them firmer in texture.
Freezer
Storage Time: Up to 3 months
How: Wrap individual bars in plastic wrap or foil, then place them in a freezer-safe bag or container. Remove as much air as possible to prevent freezer burn.
To Thaw: Let thaw at room temperature for about 30 minutes, or microwave for 10–15 seconds.
Perfect for meal prep, bake sales, or keeping a sweet stash on hand!
Reheating Tips (Optional)
Microwave for 5–10 seconds for a warm, gooey texture (especially good if they’ve been in the fridge).
If frozen, unwrap and microwave for 15–20 seconds or let thaw naturally.
If you make and love these Monster Cookie Bars or add any fun mix-in’s let me know in the comments below.
Monster Cookie Barss
These chewy monster cookie bars are packed with chocolate chips, butterscotch chips, M&Ms, creamy peanut butter, and hearty oats for the ultimate sweet and salty treat. Perfect for parties, lunchboxes, or anytime cravings hit!
Ingredients
- 1/2 cup salted butter (melted)
- 1 cup brown sugar
- 2 eggs (room temperature)
- 1 tbsp vanilla extract
- 1/4 cup creamy peanut butter
- 1 cup of all-purpose flour
- 1/2 tsp of baking powder
- 1/2 tsp salt
- 1/2 cups rolled oats
- 3/4 cup M&M's (plus a few more to top)
- 1/2 cup chocolate chips
- 1/2 cup butterscotch chips