Gooey M&M Peanut Butter Cookie Bars

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Delicious, loaded cookie bars that are the perfect combination of peanut butter and chocolate. They’re ready in less than an hour and packed with mini chocolate chips, Reese’s peanut butter chips, mini Reese’s cups, and mini M&M’s.

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I’ve been craving a peanut butter treat for awhile now and I noticed that I don’t have a peanut butter cookie/cookie bar recipe on the blog yet! Considering how much I love peanut butter, this is seriously shocking.

Peanut butter cookies, ice cream, candy…you name, I love it. Reese’s and peanut butter M&M’s are two of my top favorite candies, so you’ll see me sneak them into a lot of treats that I make. Peanut butter and chocolate together is just a match made in heaven, I can’t resist!

I had a lot of ideas about the kind of peanut butter cookie bar that I wanted to make and I’m sure some of those other ideas will end up on the blog eventually. But, today, I was craving a chewy, thick cookie bar that has a peanut butter base and is loaded with all of my favorite chocolate and peanut butter toppings. For add-ins, I chose to use mini semisweet chocolate chips, Reese’s peanut butter chips, mini Reese’s cups, and mini M&M’s. 

Spoiler alert: these turned out AMAZING. The cookie bars are full of flavor, loaded with toppings, and are so soft & gooey. Take my word for it and add these to your “to bake” list immediately.

Now, before I can say “peanut butter” one more time, let’s move on to the recipe!

Read on for the full recipe for these unreal M&M Peanut Butter Cookie Bars.

One of my favorite things about cookie bars is how easy they are to make. You only need one bowl for this one  — no mixer required — so clean up is a breeze. Plus, we’re using melted butter, so this recipe comes together quickly and is really easy to follow. 

While this recipe does call for a room temperature egg and egg yolk, you can always speed up that process by running your eggs under warm water or soaking them in a bowl of warm (not boiling hot, just warm to the touch) water for about 5-10 minutes.

Before we jump in, I have one last tip — top your cookie bars with extra toppings before you bake them in the oven! The extra toppings will add more color and flavor, making them super loaded!

Ingredients you’ll need

• Unsalted butter 
• Brown sugar
• Creamy peanut butter 
• Egg + egg yolk
• Vanilla extract 
• All-purpose flour 
• Baking soda
• Salt
• Mini semisweet chocolate chips
• Reese’s peanut butter chips
• Mini Reese’s cups
• Mini M&M’s

Kitchen tools you’ll need (linking my favorites below!)

• Baking pan
• Parchment paper
• Mixing bowls 
• Measuring cups
• Whisk
• Spatula

How to make these delicious M&M Peanut Butter Cookie Bars

Line an 8 inch square baking pan with parchment paper. Spray the parchment paper with nonstick cooking spray and set aside.

Preheat the oven to 350 degrees Fahrenheit.

Melt 10 tbsp unsalted butter in the microwave or on the stove. Let the butter cool for 10-15 minutes. 

In a large bowl, whisk together the melted butter, 1 cup of brown sugar, and ⅓ cup creamy peanut butter until smooth.

Add the egg, egg yolk, and 1 tsp vanilla. Whisk until fully combined.

With a rubber spatula, fold in 1¼ cup all-purpose flour, ½ tsp baking soda, and ½ tsp salt until just combined.

Fold in ½ cup mini semisweet chocolate chips, ¼ cup Reese’s peanut butter chips, ¼ cup chopped mini Reese’s cups, and ¼ cup mini M&M’s. 

Spread the dough into the prepared baking pan, creating an even layer. Add extra toppings, if desired, and gently press in with the back of a spoon. 

Bake for about 26 minutes. The cookie bars are done when they are a light to medium golden color and jiggle ever so slightly in the center. If they are very jiggly/not set in the center, continue to bake, checking every 1-2 minutes.

Take the pan out of the oven and let the cookie bars cool and set before slicing. I recommend waiting about 1-2 hours to ensure clean slices. This recipe makes 12 (larger) or 16 (smaller) cookie bars.

Store in an airtight container at room temperature for 5 days or freeze for up to 3 months.

Tips for success

• When measuring dry ingredients, use a kitchen scale or the spoon and level method. Before scooping out dry ingredients, fluff them up and remove any clumps with a spoon. For the spoon and level method, spoon the ingredient into the measuring cup and use a flat top tool to level off the top and remove any excess. 
• To ensure these cookie bars are super soft and chewy, be careful to not overmix your dough. When adding in dry ingredients, fold in with a rubber spatula until just a few flour streaks remain, then add in your toppings.
• The cookie bars are done baking when the center has a small/slight jiggle to it. The cookie bars will continue to bake and set once they’re removed from the oven — by taking them out at this point, it will help ensure that soft, chewy texture. If the cookie bars are very jiggly (or you prefer a more well-done cookie bar), continue to bake and check every 1-2 minutes. 
• Add extra toppings! I get a lot of questions about how to improve the appearance of cookies and cookie bars — my top tip is to add MORE toppings before baking, giving them the appearance that they’re loaded with add-ins.

FAQs

Can I double this recipe?

Yes! Double the ingredients called for and bake in a 9×13 inch pan. Baking temperature will remain the same. Bake time may vary, but start at 26 minutes and check every 1-2 minutes, removing the bars from the oven when they are a light to medium golden color and have the slightest jiggle in the center.

Can I make any substitutions?

Unfortunately, I haven’t tried this recipe with dairy or flour substitutions, so I can’t say for sure how the cookie bars will turn out. If you try out a substitution, leave me a comment and let me know how they turned out. As far as toppings, feel free to substitute with your favorites!

Can I use any kind of peanut butter?

I used Jif creamy peanut butter to make these. I do not recommend using a natural peanut butter as it may be too runny.

How to store

Store the cookie bars at room temperature in an airtight container for up to 5 days or freeze for up to 3 months. If freezing, set the cookie bars on the counter and let them come to room temperature before eating.

The dreamiest, peanut butter and chocolate cookie bars. They’re full of peanut butter flavor, have the perfect texture, and are ready in less than an hour! Try them out and let me know what you think!

If you try this recipe, share and tag me on socials using @itsbrunchoklock or #itsbrunchoklock