1. Home
  2. Recipes
  3. Fudgy Monster Cookie Bars

Fudgy Monster Cookie Bars

Featured in: Sweet Treats for Every Occasion

Fudgy Monster Cookie Bars mash up the magic of brownies and cookies. The bottom is super dense and packed with two kinds of chocolate chips for serious chocolate flavor. Then a thick layer of soft monster cookie dough rests on top—think creamy peanut butter, oats, a sprinkle of mini M&Ms, and even more chocolate. You’ll bake the brownie layer first, pop the cookie topping on, then bake again for perfect layers every time. Chill before you cut for neat squares and the best taste. Get the chocolate hit and chewy cookie goodness in each bite.
Pin it Share it Send it Print it Jump To Recipe
A woman in a kitchen smiling.
By Chloe Chloe
Updated on Tue, 13 May 2025 17:19:21 GMT
A brownie bar topped with bright M&Ms, oats, and melty chocolate chips. Pin it
A brownie bar topped with bright M&Ms, oats, and melty chocolate chips. | cookitdelish.com

Chocolate lovers, you're in for a treat! This fudgy wonder is so easy to pull off. While it bakes, it magically splits into moist cake on top with a thick, rich chocolate sauce hiding underneath. No need to fuss—just toss it in the oven and let dessert make itself.

Honestly, I whipped this up for some friends when time was tight and I had nothing else sweet in the house. The moment I scooped out a chunk and chocolate sauce oozed out, everybody gasped. Now this is my not-so-secret hack whenever I'm hit by a chocolate craving or need a crowd-pleaser in a flash.

Decadent Ingredients

  • Boiling water: Make sure it’s bubbling hot—this kicks off the magic goo underneath.
  • Oil or melted butter: Oil gives you extra moisture, but use butter if you want it richer.
  • Baking powder: Helps the cake puff up while baking.
  • Milk: Keeps everything soft and lovely, not dry.
  • Cocoa powder: Go for unsweetened here for that deep chocolate punch.
  • All-purpose flour: Yeah, this holds everything together and keeps the cake tender.
  • Granulated and brown sugars: Mixing these two means sweetness plus a caramel note that's delicious.

Casual How-To

Give the cake a break
Leave it alone for 10-15 minutes out of the oven so the sauce thickens up just right.
See if it’s done
When the top looks a bit cracked with bubbles on the sides, you’re golden.
Don’t touch while baking
Avoid stirring so your layers stay funky and perfect.
Pour hot water gently
Drizzle hot water over a spoon—don’t just dump it in so you keep layers separate.
Whip up the topping
Stir up brown and white sugar with cocoa, then dust over your batter.
Smooth out your batter
Spread the mixture into your pan as evenly as you can.
Stir the base
Start by mixing the dry stuff, then add the liquid goodies so everything blends well.
A plate of chocolate cake with chocolate chips and yellow candies. Pin it
A plate of chocolate cake with chocolate chips and yellow candies. | cookitdelish.com

Surprising Science Secrets

Once you add hot water, the sugar and cocoa melt right in and drop to the bottom, making a thick fudge sauce under the cake top. You don’t have to do anything special—it just happens!

Dreamy Ice Cream Combo

The hot, fudgy cake plays off a scoop of cold ice cream so well. You get a fun texture mix and both flavors stand out more with the temperature contrast.

Save Some for Later

If you wind up with extras, pop them in the fridge. Heat up leftovers gently to enjoy that gooey chocolate sauce all over again.

Easy Tricks for Special Touches

Mix in peppermint for a winter vibe, or toss on some berries if it’s hot out—easy ways to make it your own.

A plate of chocolate cake with chocolate chips and yellow candies. Pin it
A plate of chocolate cake with chocolate chips and yellow candies. | cookitdelish.com

Hot fudge cake is the best example of easy home baking—plain ingredients turning into wow. Serve when you’re after something cozy, rich, or just need a chocolate fix that never fails. That puddle of chocolate sauce always hits the spot!

Frequently Asked Questions

→ Why chill the monster cookie dough?
Popping the cookie dough in the fridge for 40 minutes or more makes it firmer and way easier to shape and stick on top of your brownies. It’s softer because of peanut butter, so chilling helps keep things tidy. Plus, it won’t spread too much while baking. That means you’ll actually see two fun layers.
→ Can I swap crunchy for creamy peanut butter?
Absolutely! Crunchy peanut butter is perfect if you want a little bite in the cookie layer. Small peanut bits will show up, but everything else works exactly the same.
→ Do I really have to bake the brownie part first?
Yep, you gotta. Brownies bake slower than cookies. Giving the brownie base a 15-minute jump in the oven helps both layers finish up together. Skip it, and the cookie bit could burn or your brownies might stay underdone.
→ Why wait for the bars to cool before cutting?
Cool bars are a must! Once these are cool, their chocolate flavors become even richer. They’ll hold together and slice up way cleaner. Also, they actually finish firming up as they cool. Cut too soon? You’ll get a melty mess.
→ Can I put Fudgy Monster Cookie Bars in the freezer?
For sure! Once they’ve cooled and you’ve sliced them, wrap each square in plastic and freeze them in a sealed container. They’ll stay good for three months. Let them thaw at room temp for about an hour and you’re good to eat.

Fudgy Monster Cookie Bars

Fudgy Monster Cookie Bars mix chewy chocolate brownies with a playful oatmeal and peanut butter cookie top, loaded with colorful M&Ms. It’s the dessert that makes everyone grab a second piece.

Prep Time
30 Minutes
Cook Time
40 Minutes
Total Time
70 Minutes
By Chloe: Chloe

Category: Desserts

Difficulty: Intermediate

Cuisine: American

Yield: 16 Servings (16 bars)

Dietary: Vegetarian

Ingredients

→ Brownie Base

01 1 teaspoon vanilla (pure extract)
02 5 tablespoons melted unsalted butter
03 2 whole eggs, large
04 1 extra egg yolk
05 1⅓ cups granulated white sugar
06 ⅓ cup mild-flavored oil (like vegetable or canola)
07 ½ cup all-purpose flour
08 ¾ cup cocoa powder, unsweetened and dutch process
09 1 tablespoon cornstarch
10 ¼ teaspoon table salt
11 ½ cup milk chocolate chips
12 ½ cup semi-sweet chocolate chips

→ Cookie Dough Topping

13 ¼ cup creamy peanut butter
14 ⅛ teaspoon baking powder
15 1 teaspoon vanilla extract
16 ½ cup quick-cook oats
17 ⅓ cup packed brown sugar (light or dark)
18 ½ teaspoon baking soda
19 1 medium egg, at room temperature
20 ¼ cup room-temp unsalted butter
21 ½ cup mini chocolate chips
22 ½ cup tiny M&M candies
23 ⅛ cup regular granulated sugar
24 ½ cup plain flour (all-purpose)
25 1 teaspoon cornstarch
26 ¼ teaspoon fine salt

Instructions

Step 01

Start this first since the dough has to chill a bit. Mix the dry ingredients in one medium bowl: flour, cornstarch, salt, baking soda, and baking powder. Separately in another bowl, cream the butter with the sugars using a hand mixer until all fluffy. Toss in vanilla, then add peanut butter, and blend until it's smooth. Last step—throw in the egg and mix while making sure the bowl edges stay scraped clean so the ingredients combine evenly.

Step 02

Slowly combine the dry bowl into the wet one. Do this on low speed until it just comes together—it'll seem kind of sticky, but that’s great. Fold in oats, M&M’s, and chocolate chips using a spatula to avoid overmixing. Don’t worry if you only have regular-sized candies or chips instead of minis—they work too. Cover this bowl with plastic wrap and stick it in the fridge for 40 minutes to chill out.

Step 03

Around the time the cookie dough is almost done setting, heat your oven to 325°F (165°C). Get your 9-inch square baking pan ready—spray it with nonstick spray, then line the base and two opposite sides with parchment, leaving some extra paper hanging over as lifting handles. This trick makes cleanup painless.

Step 04

First, whisk together the flour, cocoa powder, salt, and cornstarch in a medium bowl. In a bigger bowl, use a stand mixer or hand mixer to beat sugar, eggs, and the extra yolk for 5 minutes at high speed. The mixture will turn pale and super thick—don’t skip this step as it’s the secret to a great texture. While that’s mixing, melt the butter and let it cool a bit. Once the 5 minutes are up, pour the cooled butter, oil, and vanilla into the sugary eggs and stir at a slow speed until mixed.

Step 05

Now grab the big bowl and toss all the dry mix in one go. Using a spatula, fold it in gently without knocking out the air you just worked into the eggs—it’ll take a little patience. Once mostly smooth, fold the chocolate chips through. Scrape the batter into your prepped pan and spread it out evenly to cover every corner.

Step 06

Bake just the brownie batter for 15 minutes. This step is key since brownies take longer than cookies to cook. After this pre-bake, the brownie top should look slightly set but not fully cooked, which is perfect for what comes next. Don’t turn off the oven yet!

Step 07

Take the dough out of the fridge. Use your hands to squish small amounts into flat pieces and place them on top of the baked brownie base until covered. If you’ve got leftover M&M’s and chips, scatter a few more on top for extra pop. When done, pop the whole pan back in the oven for the final round.

Step 08

Bake for 20 more minutes, then lightly cover the pan with foil (to avoid browning the cookie topping too much) and finish off for another 5–10 minutes. Once cooked, take the pan out and let it rest on a cooling rack until it hits room temperature—it makes slicing and eating so much better.

Notes

  1. Say hello to these layered treats—chewy cookies meet gooey, chocolatey brownies with peanut butter, oatmeal, and candy goodness!
  2. For best results, let them cool all the way down before cutting—cooling deepens the flavor.
  3. For sharp, clean cuts, use a sharp knife and wipe it between each slice. Or chill the whole thing for 30 minutes before slicing.

Tools You'll Need

  • Square pan (9×9 inches)
  • Non-stick parchment paper
  • Hand or stand mixer (whisk attachment needed)
  • Spatula (preferably rubber)
  • Mixing bowls (at least two)
  • Baking spray
  • Rack for cooling
  • Aluminum foil

Allergy Information

Please check ingredients for potential allergens and consult a health professional if in doubt.
  • Made with gluten-containing wheat
  • Contains dairy from chocolate and butter
  • Includes peanut butter (peanuts)
  • Egg components are present
  • Might include soy (depending on chocolate chips)

Nutrition Facts (Per Serving)

It is important to consider this information as approximate and not to use it as definitive health advice.
  • Calories: 325
  • Total Fat: 17 g
  • Total Carbohydrate: 40 g
  • Protein: 5 g