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Peanut Butter Swirl Brownies

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Peanut butter and chocolate—now that’s a classic pairing that never goes out of style! Just like meat and potatoes, apple pie and vanilla ice cream, or Sonny and Cher, these two flavors were simply made for each other. There’s something undeniably magical about the rich, fudgy depth of chocolate meeting the sweet, creamy nuttiness of peanut butter.

So when I stumbled upon a Martha Stewart-inspired recipe for Peanut Butter Swirl Brownies over at Fake Ginger, I knew I had to give it a try. But instead of making the brownies completely from scratch, I decided to simplify the process with a boxed brownie mix—and wow, did it pay off! The result? Incredibly soft, chocolate brownies with pockets of sweet, creamy peanut butter swirled throughout. Every bite was perfectly gooey, rich, and indulgent, offering just the right balance of decadence and nostalgia.

peanut butter swirled brownies

Honestly, what better way to kick off the weekend than with a fresh batch of these beauties? YUM! I can already picture how much kids would love coming home from school to one of these, paired with a cold glass of milk. And let me tell you—these did not last long in my house. One bite in, and they were practically gone in a flash!

  • BROWNIE MIX (9 X 13 INCH SIZE)
  • LARGE EGGS, WATER, AND OIL NEEDED TO MAKE THE BROWNIE MIX FOR CAKELIKE BROWNIES
  • BUTTER
  • POWDERED SUGAR
  • CREAMY PEANUT BUTTER
  • SALT
  • VANILLA
brownies with peanut butter swirl

Preheat & Prep the Pan: Begin by preheating the oven according to the directions on your brownie mix package. To ensure easy removal and perfect edges, line an 8-inch square baking pan with parchment paper, leaving a 2-inch overhang on the sides. Spray the bottom of the pan with non-stick spray to prevent sticking.

Make the Brownie Batter
Prepare the brownie batter as instructed on the package, following the directions for cake-like brownies—this usually means using 3 eggs instead of 2. Stir until fully combined and smooth.

Mix the Peanut Butter Filling
In a separate bowl, mix together:

  • Butter for richness
  • Confectioners’ sugar for sweetness
  • Peanut butter for that classic nutty flavor
  • Salt to balance the sweetness
  • Vanilla extract for depth

Stir until smooth and creamy, creating a peanut butter mixture that’s easy to swirl into the brownies.

brownies with peanut butter swirl

Layer & Swirl the Peanut Butter Filling
Pour one-third of the brownie batter into the prepared baking pan, spreading it evenly with a rubber spatula. Drop dollops of half of the peanut butter filling (about 1 tablespoon each) onto the batter, spacing them about 1 inch apart—aim for about 9 dollops to distribute the flavor.

Drizzle the remaining chocolate mixture over the peanut butter filling, gently spreading it to cover the surface. Repeat the process, dropping the remaining peanut butter filling on top.

Using a butter knife, swirl the peanut butter mixture lengthwise and crosswise through the layers, creating a beautiful marbled effect. Be careful not to drag the knife too deeply, or you may cut through the parchment paper.

Bake & Cool
Place the pan in the oven and bake according to the brownie mix directions for an 8×8-inch pan. The brownies are ready when a toothpick inserted in the center comes out with a few moist crumbs but no wet batter.

Let the brownies cool in the pan for about 15 minutes before lifting them out using the parchment overhang. Place them on a wire rack to cool completely before cutting into squares. This ensures clean, even slices!

peanut butter swirl chocolate brownies

Can I use natural peanut butter instead of regular peanut butter?
Yes! However, natural peanut butter tends to be thinner and oilier, so it may not hold its shape as well when swirled. If using natural peanut butter, try chilling it slightly before adding it to the batter to help maintain the swirl effect.

How do I get the perfect peanut butter swirl?
For a beautiful swirl, drop dollops of peanut butter filling evenly over the brownie batter, then use a butter knife to gently swirl it lengthwise and crosswise. Be careful not to overmix, as you want distinct peanut butter streaks rather than fully blended batter.

How do I prevent the peanut butter from sinking to the bottom?
To keep the peanut butter swirl on top, make sure the brownie batter is thick enough before layering. If your batter is too thin, try chilling it for a few minutes before adding the peanut butter filling.

Can I add other mix-ins to this recipe?
Yes! Some delicious additions include: chocolate chips for extra richness or chopped peanuts for crunch.

How do I store peanut butter swirled brownies?
Store brownies in an airtight container at room temperature for up to 3 days. For longer storage, refrigerate them for up to a week or freeze them for up to 2 months.

What’s the best way to cut brownies cleanly?
For perfectly clean slices, let the brownies cool completely before cutting. Use a sharp knife, wiping it clean between cuts, or chill the brownies slightly before slicing.

Can I freeze peanut butter swirled brownies?
Yes! Wrap individual brownie squares in plastic wrap, then store them in an airtight container in the freezer. When ready to eat, let them thaw at room temperature or warm them slightly in the microwave.

peanut butter swirled brownies

Peanut Butter Swirl Brownies

Real Mom Kitchen

These Peanut Butter Swirled Brownies combine rich, fudgy chocolate with creamy peanut butter for the ultimate indulgent treat. With a beautifully marbled swirl, each bite delivers the perfect balance of gooey, sweet, and nutty flavors. Simple to make yet irresistibly delicious, these brownies are guaranteed to disappear fast!
5 from 2 votes
Prep Time 15 minutes
Cook Time 30 minutes
Cooling time 15 minutes
Total Time 1 hour
Course Dessert
Cuisine American
Servings 12 servings
Calories 150 kcal

Ingredients
  

BROWNIE BATTER

  • 1 pkg of brownie mix the 9 x 13 inch size
  • plus water eggs, and oil for cakelike version of brownie mix

FOR THE FILLING

  • 4 Tbsp unsalted butter melted
  • ½ cup confectioners’ sugar
  • ¾ cup smooth peanut butter
  • ¼ tsp salt
  • ½ tsp pure vanilla extract

Instructions
 

  • Preheat oven according directions on brownie mix .  Line an 8-inch square baking pan with, allowing a 2-inch overhang. Spray bottom of pan with non-stick spray.
  • Make batter according to direction on box for cake like brownies.  (This usually means just adding 3 eggs instead of 2)
  • Make filling: Stir together butter, confectioners’ sugar, peanut butter, salt, and vanilla in a bowl until smooth.
  • Pour one-third of batter into prepared pan; spread evenly with a rubber spatula. Drop dollops of half of the peanut butter filling (about 1 tablespoon each) on top of batter, spacing about 1 inch apart. I put 9 drops.
  • Drizzle remaining batter on top, and gently spread to fill pan. Drop dollops of remaining half of  filling on top. Gently swirl peanut butter filling into batter with a butter knife, running the knife lengthwise and crosswise through layers.  Be careful to not get the knife to the very bottom of the batter of you may cut the foil.
  • Bake according to brownie mix directions for 8 x 8 inch pan until a toothpick inserted into brownies comes out with a few crumbs but is not wet. Let cool slightly in pan, about 15 minutes. Lift out; let cool completely on a wire rack before cutting into squares.  Makes 9-12 brownies.

Nutrition

Serving: 1 serving | Calories: 150kcal | Carbohydrates: 9g | Protein: 4g | Fat: 12g | Saturated Fat: 4g | Polyunsaturated Fat: 2g | Monounsaturated Fat: 5g | Trans Fat: 0.2g | Cholesterol: 10mg | Sodium: 118mg | Potassium: 92mg | Fiber: 1g | Sugar: 7g | Vitamin A: 117IU | Calcium: 9mg | Iron: 0.3mg
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Keyword bars, brownies, peanut butter