These soft, gooey peanut butter cookie bars are made in one bowl in a 9×13″ pan and deliver the perfect sweet-and-salty bite. Think of them like a peanut butter twist on a s’more in cookie bar form!
Reader review ★★★★★
“They turned out amazing!! So gooey and so much delicious flavors!”
Kind of like s’mores bars but with peanut butter 👀
These bars grew out of the viral s’more cookie bars people loved on TikTok and asked for a peanut butter version. The result is a soft, peanut-butter-forward bar with toasted marshmallow pockets and melty chocolate.
Here’s why I love these:
- Soft & Gooey: The texture is tender and melt-in-your-mouth, similar to a gooey s’more.
- Sweet & Salty: Peanut butter and marshmallow balance into a classic sweet-and-salty combo.
- Packed with mix-ins: Chocolate chips, mini marshmallows, and mini Reese’s create layers of flavor and texture.
viral video
Watch me make this on Tiktok!
See how quickly these bars come together and how the marshmallows toast while baking.
@designeatrepeat Reply to @808dagreat808 sa-more fluffernutter cookie bars at your service! 🥜🍫
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what you need
Ingredient Notes & Substitutions
- Creamy peanut butter: I recommend creamy commercial peanut butter rather than natural to avoid excess oil, which can make the bars too soft.
- Cornstarch: Optional but helps create a chewier, softer texture.
- Mix-ins: Use chocolate chips, chopped peanut butter cups, or your favorite mix-ins. I often do half chocolate chips and half chopped Reese’s for the best sweet-and-salty balance.
How to Make These Fluffernutter Cookie Bars
These bars are simple and come together in one bowl—perfect for busy bakers or when you need a quick crowd-pleaser.
Make Dough
You can use a hand mixer or stand mixer with a paddle attachment. The dough will thicken near the end, so finish folding with a spatula if needed.
Press into Pan & Bake
Drop thick dough into the pan in chunks, spray your hands with nonstick spray, and press into corners for an even layer. Press extra peanut butter cups or chips on top if you want a decorative finish.
Cut
Let the bars cool before cutting; chilling in the fridge for an hour yields the cleanest slices. Use a parchment sling to lift the whole slab from the pan for neat squares.
Storage & Freezing:
- Storage: Store in an airtight container for 2–3 days for best softness; they remain edible up to 5 days but will firm slightly.
- Freezing: Marshmallow-filled treats can become sticky after thawing, but you can freeze wrapped bars for up to a month if needed. Wrap pieces individually for best results.
melissa’s tips
Tips & Variations
- Use unwrapped mini Reese’s from a bag for easy pressing into the top.
- Press extra marshmallows onto the surface before baking to get a toasty, browned top.
Frequently Asked Questions:
I haven’t tested these with natural peanut butter and I don’t recommend it, as the extra oil can make the bars overly soft and greasy.
Yes. For the best texture, make them the day of or up to one day ahead. Refrigerate before slicing if you need firmer bars.
You could layer marshmallow creme in the center instead of mixing in mini marshmallows for a different texture. It should work well, though I haven’t tested it extensively.
Looking for more 9×13 cookie bars?
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S’more Cookie Bars
-
Frosted Sugar Cookie Bars
-
Peanut Butter Blossom Bars
Fluffernutter Cookie Bars
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* Be sure to refer to the full blog post on my website for instructions & baking times!
Ingredients
- ½ cup unsalted butter, softened
- ¾ cup creamy peanut butter
- ¾ cup light brown sugar
- ¼ cup granulated sugar
- 1 large egg
- 1 egg yolk (you will use 1 whole egg + 1 extra yolk)
- 1 teaspoon vanilla extract
- ½ teaspoon baking soda
- ¼ teaspoon salt
- 1 tablespoon cornstarch (optional, for chewier texture)
- 1 ½ cups all-purpose flour
- 1 cup semi-sweet chocolate chips (or half chips + half chopped Reese’s)
- 1 cup mini marshmallows
⭐️ Before you begin! If you make this, please consider leaving a review and rating in the comments so others know how the recipe worked for you.
Instructions
- Preheat oven to 350ºF. Read tips in the post for best results.
- In a medium bowl, beat ½ cup softened unsalted butter and ¾ cup creamy peanut butter on medium for 20–30 seconds until combined.
- Add ¾ cup light brown sugar and ¼ cup granulated sugar; beat on medium 20–30 seconds until creamy. Avoid overmixing.
- With the mixer on low, add 1 large egg, 1 egg yolk, 1 teaspoon vanilla, ½ teaspoon baking soda, ¼ teaspoon salt, and 1 tablespoon cornstarch. Stir to combine. Slowly add 1½ cups all-purpose flour and mix until just incorporated.
- Fold in 1 cup semi-sweet chocolate chips and 1 cup mini marshmallows.
- Grease and line a 9×13 light-colored metal pan with parchment (create a parchment sling to lift bars out). Spread dough into an even layer.
- If desired, press extra chips or peanut butter cups into the top.
- Bake 16–18 minutes or until edges are lightly brown, marshmallows are toasted, and the center no longer looks wet. Cool at least 30 minutes before cutting; refrigerate about 1 hour for clean slices.
Notes from Melissa
Freezing: Freeze in an airtight container or freezer bag for up to 1 month. Wrap individual bars before freezing for best freshness.
Nutrition
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📸 Photography by Jane Campbell for Design Eat Repeat®