These Marshmallow Peanut Butter Brownies should be your next decadent go-to treat! They combine rich and chewy, chocolatey brownies with marshmallow fluff and a peanut butter filling swirled all over the top! They are a fantastic recipe from my friend Sarah Kieffer's new cookbook, 100 Cookies that are perfect for any brownie lover in your life!
6 reasons why you should make these marshmallow peanut butter brownies
- Rich and chocolatey brownies that are right in between fudgy and cakey—the best of both worlds!
- You don't need your hand mixer OR stand mixer.
- Swirled peanut butter and marshmallow on top!
- Easy prep and takes about 26-32 minutes to bake.
- Chocolate, peanut butter, and marshmallow together is a heavenly trio of flavors!
- They're from Sarah Kieffer's new cookbook, 100 Cookies!
about the author: Sarah Kieffer
Sarah is a legend when it comes to cookies and brownies! She is most widely known for her pan-banging cookies, which she dedicates an entire chapter to in her latest cookbook, 100 Cookies.
She also brings back her popular "My Favorite Brownies" recipe, which is from her first book, The Vanilla Bean Baking Book. It's also the base recipe I used to make these marshmallow peanut butter brownies.
If you love brownies and cookies (and really any dessert), I definitely recommend getting both her cookbooks, checking out her blog, The Vanilla Bean Blog: A Baker's Soliloquy, or give her a follow over on Instagram!
And just a little side note, Sarah is one of the coolest and kindest people I've met in the baking blog world. I'm so proud of her and all she has accomplished!
baking tools needed
Here are the baking tools I recommend for a successful marshmallow peanut butter brownie making experience.
- 9 x 13 inch baking pan. My Nordic Ware metal pan is my go-to baking pan for all my sheet cakes, rice krispie treats, and these brownies!
- Baker's Joy Baking Spray. I swear by this for greasing any of my baking pans. You can alternatively use a light coating of butter and dusting of flour or vegetable shortening and flour.
- Parchment paper. Not required, but it definitely helps with removing the brownies to cool and cut.
- Mixing bowls. You'll need at least 3 for this recipe. Two smalls and a medium is good.
- Saucepan. This is for melting the chocolate and butter together. I used my Dansk 1 quart hot cocoa pot.
- Whisks and spatulas. The whisks come in handy for mixing the dry and wet ingredients. When combining the two, a spatula does a good job there as well as when you pour the batter into the pan.
- Wire cooling rack. For cooling of the brownies, of course.
- Large knife. A sharp large knife is always handy for cutting brownies!
how to make these marshmallow peanut butter brownies
I know brownies are probably one of the easiest recipes to make, but for fun, here's a general outline of how to make these brownies with peanut butter filling and marshmallow fluff. The full recipe is below or you can find these in Sarah's new 100 Cookies cookbook!
Make the peanut butter filling. You can easily do this in a small bowl stirring it together with either a whisk or spatula. I prefer to do this step first before I make the brownies. You will need creamy peanut butter, confectioners' sugar, unsalted butter, and salt.
Whisk the dry ingredients together. This includes the all-purpose flour, salt, and baking powder.
Whisk the wet ingredients. Do this in a separate mixing bowl for the eggs, canola oil, granulated and brown sugars, and vanilla extract.
Melt the butter and chocolate. Make sure you to chop up the chocolate or break it up into smaller pieces and use a small, heavy bottom sauce pan. Add this to the wet ingredients and mix until well blended.
Add the dry ingredients to the wet. Mix until it is just combined.
Pour the brownie batter into the prepared pan. Don't forget to use your spatula to get all the batter out of the bowl.
Dollop then swirl. Alternate between dolloping the peanut butter filling and marshmallow fluff. Then gently swirl together with the brownie batter using a butter knife.
Bake then cool. These brownies will take anywhere from 26-32 minutes at 350ºF. Cool on a wire rack after. Make sure they are cooled completely before cutting.
can I use the microwave to heat the chocolate and butter?
Yes! Heat for 45 - 60 seconds at medium power. Stir, then repeat until both ingredients have fully melted and is smooth. Add in the cocoa powder after.
will these brownies keep at room temperature?
Yes! For up to 2 days stored in a sealed food container. You can also keep them in the refrigerator for a day or two longer.
my top marshmallow peanut butter brownie making tips
Use the parchment sling. This not only is helpful when removing the brownies from the pan to cool, but makes it easier to cut them as well!
Mix up the peanut butter filling first. This is just a little it of a time saver tip. Once you pour the brownie batter into the pan, you'll want to dollop on the peanut butter filling and marshmallow fluff immediately after.
Warm up the marshmallow fluff. I found that by heating it up in the microwave for 15 seconds helped with dolloping it onto the top of the brownies.
Swirling 101. Just skim the top of the brownies as you swirl. I went a little too crazy with the swirling and ended up pushing most of the marshmallow fluff to the inside. They still tasted incredibly good, and it was nice seeing the marshmallow peak through when you took a bite. They're just not as pretty as Sarah's!
Marshmallow Peanut Butter BrowniesAuthor:
peanut butter filling
- ½ cup Creamy Peanut Butter
- ¼ cup Powdered Sugar
- 2 tablespoon Unsalted Butter (room temperature)
- Pinch of Salt
- 1 cup + 2 tbsp All-Purpose Flour
- ¾ teaspoon Salt
- ½ teaspoon Baking Powder
- 4 Large Eggs (room temperature)
- 1 ½ cups Granulated Sugar
- ½ cup Brown Sugar (packed)
- ½ cup Canola Oil
- 2 teaspoon Pure Vanilla Extract
- 8 tablespoon Unsalted Butter
- 8 oz Bittersweet Chocolate (chopped)
- ¼ cup Dutch Process Cocoa Powder
- ½ cup Store-Bought Marshmallow Fluff
peanut butter filling
- In a medium bowl, mix together the peanut butter, powdered sugar, unsalted butter, vanilla, and salt until combined and completely smooth. Set to the side.½ cup Creamy Peanut Butter, ¼ cup Powdered Sugar, 2 tablespoon Unsalted Butter, Pinch of Salt
- Adjust an oven rack to the middle of the oven. Preheat the oven to 350ºF (180ºC). Grease a 9 by 13 inch (23 by 33 cm) baking pan and line with a parchment sling.
- In a small bowl, whisk together the flour, salt, and baking powder.1 cup + 2 tablespoon All-Purpose Flour, ¾ teaspoon Salt, ½ teaspoon Baking Powder
- In a small bowl, whisk together the eggs, granulated and brown sugars, canola oil, and vanilla.4 Large Eggs, 1 ½ cups Granulated Sugar, ½ cup Brown Sugar, ½ cup Canola Oil, 2 teaspoon Pure Vanilla Extract
- Place the butter and chocolate in a small, heavy-bottom saucepan set over low heat and melt together, stirring frequently to prevent the chocolate from scorching. Continue cooking until the mixture is smooth. Off the heat, add the cocoa powder to the chocolate and whisk until completely combined.8 tablespoon Unsalted Butter, 8 oz Bittersweet Chocolate, ¼ cup Dutch Process Cocoa Powder
- Add the chocolate mixture to the sugar-egg mixture and whisk until smooth. Add the flour mixture and stir until just combined.
assembling the marshmallow peanut butter brownies
- Pour the brownie batter into the prepared pan. Dollop the peanut butter filling and the marshmallow creme over the top, alternating the two. Drag the tip of a butter knife through the batter, creating swirls.½ cup Store-Bought Marshmallow Fluff
- Bake until the sides of the brownies have set, the top is starting to crackle and look glossy, and a wooden skewer or toothpick inserted into the center comes out with crumbs, 26 to 32 minutes. The batter on the toothpick should not be wet, but should have a good amount of crumbs clinging to it.
- Transfer the pan to a wire rack and let cool completely. Use the parchment sling to gently lift the brownies from the pan. Cut them into bars and serve. Store brownies in an airtight container at room temperature for up to 2 days.