These 4-Ingredient Peanut Butter Swirl Brownies have a fudgy chocolate base and thick ribbons of creamy peanut butter. Boxed fudge brownie mix keeps the prep simple, and a few broad strokes with a butter knife give each square a different marbled pattern.
What You’ll Need
- Fudge brownie mix. Use one 18-ounce box. The eggs and melted butter below are the additions for this recipe.
- Large eggs. Two eggs bind the batter and help the brownies hold together when sliced.
- Melted butter. Let it cool slightly before stirring it into the mix with the eggs. The finished batter should be thick and spreadable.
- Creamy peanut butter. Warm it just until it drizzles off a spoon. This makes it easier to create distinct ribbons across the chocolate batter.
How to Swirl Peanut Butter into Brownies
Spread the brownie batter evenly in the prepared dish, reaching into the corners with a spatula. Drizzle the warm peanut butter across the top in wide lines. Run a butter knife through the lines in a few broad S-shaped strokes, dipping the blade slightly below the surface so some peanut butter reaches into the batter.
Stop while the chocolate and peanut butter are still clearly visible. A few passes create thicker ribbons that show up when you cut the brownies.
How to Tell When the Brownies Are Done
Bake at 350°F (175°C) for 28–35 minutes. Look for set edges and test a chocolate spot near the center with a toothpick. A few moist crumbs mean the brownies are ready. If the toothpick comes out coated in wet chocolate batter, give them a few more minutes and check again.
Test away from a thick peanut butter ribbon, since melted peanut butter can cling to the toothpick even when the chocolate batter is baked. The thinner layer in a 9-inch dish may finish sooner than the thicker layer in an 8-inch dish.
Serving and Storage
Cool the brownies in the dish before cutting into 12 pieces. Wipe the knife between cuts to keep the marbled tops tidy. Serve the brownies plain or add a scoop of vanilla ice cream for a plated dessert.
Once cool, store them in an airtight container. If you stack the brownies, slip a sheet of parchment between the layers to protect the swirled tops.
Frequently Asked Questions
Do I prepare the brownie mix according to the box?
For this recipe, stir the dry mix directly into the eggs and melted butter using the amounts in the recipe card.
Why did my peanut butter swirl disappear?
Repeated strokes can blend the peanut butter into the chocolate. Use a few broad passes and leave some ribbons untouched on top.
Can I use crunchy peanut butter?
Yes. The pieces will add crunch and give the swirl a more textured look. Warm it gently so it’s easy to drizzle.
4-Ingredient Peanut Butter Swirl Brownies Recipe Card
Fudgy chocolate brownies with creamy peanut butter ribbons.
- Prep time — About 10 minutes
- Bake time — 28–35 minutes
- Yield — 12 brownies
- Pan — 8-inch or 9-inch square oven-safe glass baking dish
Ingredients
- 1 box (18 ounces) fudge brownie mix
- 2 large eggs
- ½ cup butter, melted and slightly cooled
- ¾ cup creamy peanut butter, warmed until pourable
Instructions
- Preheat the oven to 350°F (175°C). Lightly grease an 8-inch or 9-inch square oven-safe glass baking dish.
- Stir together the dry brownie mix, eggs, and melted butter until a thick, smooth batter forms.
- Spread the batter evenly in the prepared dish.
- Drizzle the warmed peanut butter over the batter. Draw a butter knife through it in a few broad strokes to create a marbled pattern.
- Bake for 28–35 minutes, until the edges are set and a toothpick inserted into a chocolate spot near the center comes out with moist crumbs.
- Cool in the pan before slicing into 12 brownies.