Imagine biting into a thick, fudgy brownie with a ribbon of silky peanut butter marbled across the top. Every square is part brownie, part peanut butter fudge, with crackly edges and a soft center that almost melts on your tongue.

These Peanut Butter Swirl Brownies look bakery-fancy, but they’re incredibly simple to make at home. The brownie base bakes up rich and chocolatey, the peanut butter layer stays creamy, and the pretty swirl pattern makes them perfect for parties, holidays, or an everyday “just because” treat.

Why You’ll Love These Peanut Butter Swirl Brownies

Peanut butter and chocolate are a classic flavor duo, and these brownies deliver that combo in the coziest way. You get deep cocoa flavor, real melted chocolate, and a creamy swirl that stays soft even after the brownies cool.

They’re special enough for a celebration but easy enough to bake on a busy weeknight. No mixer, no complicated steps, just one pan of gooey, crowd-pleasing goodness that disappears fast from dessert tables and lunch boxes.

What Kind of Peanut Butter Works Best for Swirl Brownies?

For the smoothest, most defined swirl, use a creamy peanut butter that’s labeled “regular” or “no-stir.” These types are stabilized, so they hold their shape as the brownies bake and don’t separate into oily streaks.

Natural peanut butter, the kind that separates in the jar and needs stirring, can taste great but tends to be runnier. If you’d like to use it, make sure it’s well mixed and be prepared for a softer, less defined swirl. You can also thicken it with a little powdered sugar to help it behave more like conventional peanut butter.

Ingredients

Before you start baking, take a moment to understand what each ingredient brings to these brownies. Knowing the “why” makes it easier to swap or adjust things without losing that fudgy, swirly magic.

Unsalted butter – Adds richness and moisture, helping the brownies stay fudgy instead of cakey.
Semi-sweet chocolate – Melts into the butter for a deep chocolate backbone and glossy texture.
Granulated sugar – Sweetens the brownies and helps create that shiny, crackly top.
Light brown sugar – Adds a hint of caramel flavor and extra chewiness.
Large eggs – Bind the batter together and give the brownies structure while keeping them tender.
Vanilla extract – Rounds out both the chocolate and peanut butter flavors.
All-purpose flour – Provides structure; just enough to hold everything together without drying the brownies out.
Unsweetened cocoa powder – Boosts the chocolate flavor and contributes to the rich color.
Fine sea salt – Balances sweetness and intensifies both chocolate and peanut butter notes.
Creamy peanut butter – Creates the luscious swirl; a no-stir style works best.
Powdered sugar – Sweetens and thickens the peanut butter mixture so it swirls cleanly.
Milk or heavy cream – Loosens the peanut butter swirl to a spoonable, drizzle-able consistency.
Additional vanilla for the swirl – Adds warmth and depth to the peanut butter layer.
Pinch of salt for the swirl – Keeps the peanut butter from tasting flat or overly sweet.
Semisweet chocolate chips (optional) – Folded into the batter for extra chocolate pockets in every bite.

How To Make Peanut Butter Swirl Brownies

This brownie batter comes together quickly, so it helps to have your pan lined, ingredients measured, and oven preheating before you begin. Once the base and swirl are ready, you’ll layer, marble, and bake.

Step 1: Prep the Pan and Oven

Line a square baking pan with parchment paper, letting it hang over the edges to create a sling. Lightly grease the parchment and any exposed sides of the pan. Preheat your oven so it’s fully hot by the time the batter is ready—this ensures the brownies bake evenly with set edges and a soft middle.

Step 2: Make the Fudgy Brownie Base

Gently melt the butter and semi-sweet chocolate together, either in a saucepan over low heat or in short bursts in the microwave. Stir until smooth and glossy, then let the mixture cool slightly so it doesn’t scramble the eggs.

Whisk in the granulated sugar and brown sugar until the mixture looks thick and shiny. Add the eggs one at a time, whisking well after each addition, then stir in the vanilla. Switch to a spatula and fold in the flour, cocoa powder, and salt just until no dry streaks remain. Overmixing at this stage can make the brownies tough instead of fudgy. If you’re using chocolate chips, fold them in now.

Step 3: Stir Together the Peanut Butter Swirl

In a separate bowl, whisk the creamy peanut butter with powdered sugar, a splash of milk or cream, vanilla, and a pinch of salt. The mixture should be smooth and slightly pourable—thicker than pancake batter but loose enough to drizzle off a spoon. If it feels too stiff, add a tiny bit more milk; if it seems too runny, sprinkle in a little extra powdered sugar.

Step 4: Layer and Swirl

Spread most of the brownie batter into the prepared pan, smoothing it into an even layer that reaches the corners. Drop spoonfuls of the peanut butter mixture over the top, then add small dollops of the remaining brownie batter in the spaces between.

Use a butter knife or a skewer to gently drag through the batter in swoops and figure-eights, creating a marbled pattern. Try not to over-swirl; a few deliberate passes are enough to blend the two batters while still leaving visible ribbons of peanut butter.

Step 5: Bake Until Set at the Edges

Slide the pan into the preheated oven and bake until the edges look set and slightly pulled away from the sides, while the center still has a little jiggle and a toothpick inserted near the middle comes out with a few moist crumbs. Remember that brownies continue to cook from residual heat after you pull them from the oven.

Step 6: Cool, Slice, and Serve

Place the pan on a wire rack and let the brownies cool completely. This helps the swirl firm up and makes slicing much easier. Once cool, use the parchment sling to lift the slab from the pan and cut into neat squares with a sharp knife, wiping the blade clean between cuts for picture-perfect edges.

Serving These Peanut Butter Swirl Brownies

Serve these brownies just as they are for a rich afternoon treat, or warm individual squares for a few seconds in the microwave to bring back that fresh-from-the-oven gooeyness. They’re fantastic with a scoop of vanilla ice cream, a drizzle of chocolate sauce, or a handful of chopped peanuts for crunch.

This batch makes about 16 brownies, which can comfortably serve 12–16 people depending on how generous you slice them and what else is on the dessert table. They’re ideal for potlucks, school parties, bake sales, or keeping in the kitchen for sweet snack emergencies.

Storing Peanut Butter Swirl Brownies

Once completely cool, store the brownies in an airtight container. At room temperature, they stay soft and delicious for about 3 days. If your kitchen is warm or you prefer a firmer texture, you can refrigerate them; the brownie base will become a bit denser and fudgier, and the peanut butter swirl will set slightly more.

For longer storage, wrap individual squares tightly in plastic wrap, then place them in a freezer-safe bag or container. Freeze for up to 2 months. When you’re ready to enjoy one, thaw at room temperature or warm gently in the microwave. Freezing them in single portions makes it easy to satisfy a chocolate craving without baking a new batch every time.

If you plan to stack brownies in a container, slip parchment paper or wax paper between the layers to protect the swirls and keep them from sticking together.

Frequently Asked Questions

Can I use natural peanut butter in these brownies?
Yes, but the swirl may not hold its shape as well. Natural peanut butter is usually thinner and oilier, which can cause the swirl to spread or bake up greasy. If you’d like to use it, stir the jar very well, then mix the peanut butter with a bit more powdered sugar to thicken it before swirling.

How do I get clean, sharp slices?
Let the brownies cool completely before cutting—chilling them briefly in the fridge makes slicing even easier. Use a large, sharp knife and wipe the blade clean with a warm, damp cloth between cuts. This keeps the peanut butter and chocolate layers from smearing together.

Can I make these brownies ahead of time?
Absolutely. These brownies are a great make-ahead dessert because the flavors deepen after a day. Bake them, cool completely, then store covered at room temperature or in the fridge. Slice just before serving or cut and store in an airtight container with parchment between layers.

Can I double the recipe for a larger pan?
Yes, you can double the ingredients and bake the batter in a 9×13-inch pan. The brownies will be slightly thinner but still rich and fudgy. Start checking for doneness a few minutes earlier than you would for a smaller pan since a larger surface area can bake a bit faster.

How do I know when the brownies are done baking?
Look for edges that are set and slightly pulling away from the pan, while the center still looks a little soft. A toothpick inserted an inch from the edge should come out mostly clean, while one in the center should have a few moist crumbs. If the toothpick is completely wet, give them a few more minutes; if it’s totally dry, they may be overbaked.

Want More Brownie and Dessert Bar Ideas?

If these Peanut Butter Swirl Brownies have you craving more bar desserts, you’ll love exploring some of these other treats:

Pumpkin Cheesecake Swirl Brownies – A fall-inspired mash-up with pumpkin spice and tangy cheesecake ribbons.
Healthy Cottage Cheese Protein Brownies – A higher-protein option when you want something chocolatey but a little lighter.
Apple Brownies – Simple Autumn Treat – Soft, cinnamon-kissed squares packed with tender apple pieces.
Cranberry Bars with Cream Cheese Frosting – Sweet-tart bars with a creamy topping that are perfect for holidays.

Bake a pan for every season or mix and match a few of these recipes for a dreamy dessert bar spread at your next gathering.

Save This Pin For Later

📌 Save these Peanut Butter Swirl Brownies to your Pinterest dessert board so you can bake them again whenever the chocolate–peanut butter cravings hit.

When you make them, feel free to put your own spin on the swirl. Add a handful of chocolate chips on top, use crunchy peanut butter for extra texture, or drizzle a little melted chocolate over the cooled brownies.

I love hearing how you customize them. Did you go extra fudgy, add nuts, or double the peanut butter? Tell me all about it in the comments and share your tips so we can all bake even better brownies together. And if you’re looking for more sweet inspiration, follow Life With Livia on Pinterest where I share new recipes and dessert ideas all the time.

Peanut Butter Swirl Brownies