Introduction

I make these Gooey S’mores Stuffed Chocolate Brownie Bars when I want a dessert that combines the two best things I know — fudgy from-scratch brownies and gooey s’mores — into one bar that tastes like a campfire dream baked into a pan.
What makes this s’mores brownie bars recipe so irresistible is the layers. A graham cracker crust presses into the bottom, a rich dark chocolate brownie batter covers it, and a layer of mini marshmallows and chocolate chunks gets pressed in halfway through baking so everything melts together into one cohesive, gooey, spectacular result.
These are the bars I bring to potlucks and watch disappear in minutes. If you love a fudgy from-scratch brownie in a different format, this rich double chocolate chunk brownie uses the same melted dark chocolate base baked into a classic slab that’s just as addictive.

Why You’ll Love This Recipe

These Gooey S’mores Stuffed Chocolate Brownie Bars deliver three iconic layers in every single bite — buttery graham cracker crust, fudgy dark chocolate brownie, and gooey toasted marshmallow.
The marshmallows toast slightly in the oven as they melt, giving the top a golden, slightly crispy surface that looks and tastes incredible.
This easy chocolate brownie bars with s’mores filling recipe uses one bowl for the brownie batter and comes together in about 40 minutes total.
They slice cleanly once cooled and hold their shape beautifully, making them easy to transport and plate for any gathering.
They work year-round but feel especially right around summer, fall, and the holiday season when s’mores flavors are everywhere.

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About the Ingredients

Graham Cracker Crust

Crushed graham crackers mixed with melted butter and a little sugar pressed into the bottom of the pan form the crust of these Gooey S’mores Stuffed Chocolate Brownie Bars. The crust adds a slightly sweet, crunchy base that contrasts perfectly with the fudgy brownie layer above it. Press it firmly and evenly so it holds together when sliced.

Dark Chocolate and Butter

Good quality dark chocolate melted with butter creates the rich, fudgy brownie batter. Use chocolate with at least 60% cocoa for the deepest flavor — the chocolate is the backbone of this entire s’mores brownie bars recipe so quality matters. Sally’s Baking Addiction’s seriously fudgy homemade brownie guide confirms that using melted chocolate rather than cocoa powder alone is what creates that dense, intensely fudgy texture that sets a great brownie bar apart from a mediocre one.

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Sugar and Brown Sugar

A combination of granulated and brown sugar gives the brownie layer its shiny crackly top and fudgy density. The brown sugar adds a subtle molasses note that deepens the chocolate flavor in these Gooey S’mores Stuffed Chocolate Brownie Bars.

Eggs

Three eggs plus one egg yolk give the batter richness and that characteristic shiny top. Room temperature eggs incorporate more smoothly and help the batter emulsify properly for a better texture throughout.

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Mini Marshmallows

A full layer of mini marshmallows pressed into the partially baked brownie is what makes this easy chocolate brownie bars with s’mores filling recipe so special. They sink slightly into the warm batter, melt around the edges, and toast on top into golden gooey pockets that make every bite feel like a campfire treat.

Chocolate Chunks

Roughly chopped dark chocolate pressed into the marshmallow layer adds extra gooey chocolate pockets throughout the bar. They melt into the marshmallow during the final minutes of baking for an indulgent, layered result.

Flour and Cocoa

A small amount of all-purpose flour and Dutch-process cocoa keeps the brownie fudgy rather than cakey. Less flour means more fudge — this recipe uses the minimum needed for structure.

Tips and Tricks

Press the graham cracker crust firmly and evenly into the pan so it holds together when sliced. A flat-bottomed measuring cup works perfectly for pressing.
Pull the brownie from the oven halfway through baking — at about 12 minutes — to add the marshmallow and chocolate chunk layer. This prevents the marshmallows from burning before the brownie is done.
Let these Gooey S’mores Stuffed Chocolate Brownie Bars cool completely in the pan before slicing. The marshmallow layer needs to set or it will pull apart messily when cut.
Line the pan with parchment paper with overhang on two sides for easy lifting and clean slicing.

Pro Tips

Add a teaspoon of espresso powder to the brownie batter for a mocha depth that makes the chocolate taste even more intense in this s’mores brownie bars recipe.
Torch the marshmallow top with a kitchen torch for 10 to 15 seconds right after the bars come out of the oven for a more dramatic toasted campfire look.
Sprinkle a generous pinch of flaky sea salt over the marshmallow top immediately after baking — the salt against the sweet toasted marshmallow and dark chocolate is genuinely one of the best flavor combinations in these easy chocolate brownie bars with s’mores filling.
Freeze the cut bars individually for up to 2 months. They thaw in about 20 minutes at room temperature and taste just as good as fresh.

Step-by-Step Instructions

Preheat oven to 350°F. Line a 9×13-inch baking pan with parchment paper leaving overhang on two sides.
Make the crust: combine 1½ cups of crushed graham crackers, 5 tablespoons of melted butter, and 2 tablespoons of granulated sugar. Mix until the texture resembles wet sand. Press firmly into the bottom of the prepared pan.
Bake the crust for 8 minutes. Remove and set aside to cool slightly.
Make the brownie batter: melt ¾ cup of unsalted butter with 5 oz of chopped dark chocolate in a medium saucepan over low heat, stirring until smooth. Cool for 5 minutes.
Whisk ¾ cup of granulated sugar and 2 tablespoons of brown sugar into the chocolate mixture.
Add 3 eggs plus 1 egg yolk and 1 teaspoon of vanilla extract. Whisk vigorously for 2 minutes until glossy.
Fold in ⅓ cup of all-purpose flour, 3 tablespoons of Dutch-process cocoa powder, and ½ teaspoon of salt until just combined.
Pour the brownie batter over the pre-baked graham cracker crust and spread evenly.
Bake for 12 minutes.
Pull the pan out of the oven. Scatter 2 cups of mini marshmallows and ¾ cup of roughly chopped chocolate chunks evenly over the partially baked brownie.
Return to the oven and bake for another 10 to 12 minutes until the marshmallows are golden and the brownie edges are set.
Cool completely in the pan — at least 1 hour — before lifting out and slicing into bars.

Variations

Peanut butter s’mores version: Swirl 3 tablespoons of peanut butter into the brownie batter before baking for a chocolate peanut butter s’mores bar in these Gooey S’mores Stuffed Chocolate Brownie Bars.
White chocolate version: Use white chocolate chunks instead of dark for a sweeter, creamier filling that contrasts beautifully with the dark chocolate brownie layer.
Caramel s’mores version: Drizzle warm caramel sauce over the marshmallow layer before the final bake for a salted caramel s’mores brownie bar that is completely over the top.
Nutella layer: Spread a thin layer of Nutella over the graham cracker crust before adding the brownie batter for a hazelnut chocolate note throughout this s’mores brownie bars recipe.
Campfire version: Toast the finished bars under the broiler for 60 to 90 seconds for an even more aggressively toasted marshmallow top that looks and tastes exactly like a campfire s’more.

How to Store

Store Gooey S’mores Stuffed Chocolate Brownie Bars in an airtight container at room temperature for up to 3 days. The marshmallow layer firms up slightly as they sit but stays gooey and delicious.
Refrigerate for up to 5 days — let them come to room temperature or warm briefly in the microwave for 10 to 15 seconds before eating to restore the gooey marshmallow texture.
These bars freeze beautifully. Wrap individual bars tightly in plastic wrap and freeze for up to 2 months. Thaw at room temperature for 20 minutes before eating.

Frequently Asked Questions

Why are my Gooey S’mores Stuffed Chocolate Brownie Bars hard to slice cleanly?

They weren’t cooled long enough. The marshmallow needs at least 1 full hour to set before slicing. Use a sharp knife dipped in hot water and dried between each cut for the cleanest result.

Can I use a box brownie mix for this s’mores brownie bars recipe?

Yes. Prepare a box brownie mix according to package directions and pour it over the pre-baked graham cracker crust. Follow the same two-stage baking process with the marshmallows added halfway.

Why did my marshmallows burn?

They were added too early or the oven temperature was too high. Pull the pan at the 12-minute mark to add the marshmallows — not before. If they’re browning too fast, tent loosely with foil for the last few minutes.

Can I make these easy chocolate brownie bars with s’mores filling ahead of time?

Yes. Bake and cool them completely, then store covered at room temperature for up to 3 days. They actually slice more cleanly after sitting overnight as everything sets fully.

Do I have to pre-bake the graham cracker crust?

Yes. Pre-baking for 8 minutes sets the crust so it stays firm and distinct under the brownie batter rather than turning soggy.

Can I make these in an 8×8-inch pan instead?

Yes. Use half the recipe in an 8×8-inch pan and reduce the total baking time by 5 to 7 minutes. Watch the marshmallow layer closely for browning.

Can I torch the marshmallow top instead of baking it?

You can torch the marshmallow after baking for extra color, but the marshmallows still need to be baked into the brownie for them to melt properly in these Gooey S’mores Stuffed Chocolate Brownie Bars.

What can I serve these with?

These bars are incredible on their own but even better with a scoop of vanilla ice cream. For another chocolate and marshmallow dessert to serve at the same gathering, these s’mores crescent rolls use the same classic s’mores flavors in a completely different format that comes together in under 20 minutes.