S'mores Brownies Using Boxed Brownie Mix are what I make when I want the campfire vibe without the mess. Fudgy brownie base, gooey marshmallow on top, and enough graham cracker crunch to actually taste like a s'more. Talk about easy desserts!
The brownie batter isn't the hard part. The timing is. Add the topping too early, and the marshmallows burn before the brownies are done. Add it too late, and you end up with a pile of toppings that doesn't melt into that sticky, pull-apart bite.
If you've ever had burnt marshmallows, chocolate that stayed chunky, or graham crackers that went soft, this is the simple fix.
What Makes These Taste Like Real S'mores
You need three textures working together:
- Fudgy base: Brownies baked until they are set at the edges but still soft in the center.
- Melty layer: Chocolate that warms enough to get creamy when you bite into it.
- Toasty top: Marshmallows browned just a little so you get that campfire flavor.
Graham crackers matter here too, but they behave differently depending on when they go in. If they sit in the oven the whole time, they can go stale and soft. If they go on at the very end, they stay crunchy and snappy, which is exactly what you want.
The Timing Trick So Marshmallows Don't Burn
Bake the brownies most of the way through before adding anything on top. You'll know you're in the right spot when the edges look set and slightly pulled from the pan, but the center still looks a little softer than the edges.
One more cue I use: a toothpick in the center should come out with thick, fudgy crumbs, not wet batter, but not totally clean either. That's the sweet spot, because the topping step finishes the bake.
If you're using a glass 9×13 pan like I did - glass tends to bake a little more gently, so don't be surprised if it needs a few extra minutes compared to a metal pan. Either way, start checking early so you don't accidentally overbake.
Topping Order - Yes, It Matters
For the best bite, layer like this:
- Chocolate pieces first (so they warm against the hot brownie surface)
- Mini marshmallows next (they melt into gaps and toast quickly)
- Graham crackers last (so they stay crisp and don't disappear into the melt)
If you want more crunch, use larger graham pieces. If you want a more bar-style top, crush them smaller so they fill in the spaces.
How to Toast the Marshmallows Without Turning Them Bitter
You can finish these two ways, depending on how toasty you want the top.
Oven finish: Put the pan back in the oven just long enough for the marshmallows to puff and the chocolate to look glossy. This is the easiest method and hardest to mess up.
Quick broil: If you want that real campfire look, broil briefly, but don't walk away. Marshmallows go from golden to black fast. I pull the pan as soon as I see a few browned spots.
If your broiler runs hot, keep the pan on a lower rack.
Cooling
These slice best when they cool at least a little bit. If you cut them too soon, the topping can slide and the brownies can look messy (still delicious, just less photogenic).
If you want cleaner squares:
- Let the pan cool until warm, not hot
- Use a sharp knife and wipe between cuts
- For super clean cuts, chill briefly, then cut
Make-Ahead and Storage
These are best the day they're made, when the topping is still a little gooey and the graham crackers have bite.
To store:
- Cover tightly and keep at room temperature for a day or two
- If you refrigerate, the brownies firm up (still great), but the topping loses some of the gooey pull
To rewarm a piece, a few seconds in the microwave brings back the s'mores vibe.
Variations That Actually Work
- Extra chocolate: Add a handful of chocolate chips or more chopped chocolate on top.
- More s'mores flavor: Sprinkle a little extra graham on after baking (for fresh crunch).
- Less sweet: Use dark chocolate instead of milk chocolate.
FAQs
Yes. A fudgy mix works best. If the box has directions for "cakey vs fudgy," choose the fudgy option.
They likely melted for too long. Add them during the final minutes, not at the beginning.
They were added too early or cut too small. Add graham crackers last and keep pieces larger for crunch.
You can, but bake time changes a lot. A 9×13 is the easiest for predictable timing and topping coverage
What to Serve With These
- Homemade Ice Cream in a Bag (this one is fun if kids are around)
- Biscoff Hot Chocolate if you want a cozy dessert night
If you're on a dessert-bar kick, you can also browse my homemade bars recipes for more easy treats like this.
📖 Recipe
S'mores Brownies Using Boxed Brownie Mix
Video
Ingredients
Brownie base
- 1 box family-size brownie mix for a 9×13 pan about 18.3 oz / 520 g
- 2 large eggs
- ⅓ cup vegetable oil
- ⅓ cup water
S'mores topping
- 6 graham cracker sheets broken into bite-size pieces
- 2 cups mini marshmallows
- 6 oz milk chocolate chopped (equivalent to about 12 snack-size bars / ~153 g)
Instructions
- Heat oven to the temperature listed on your brownie mix box for a 9×13. Grease a 9×13 dish (or line a metal pan with parchment).
- In a bowl, stir together brownie mix, eggs, oil, and water until just combined.
- Spread batter in pan. Bake according to the box time, checking a few minutes early (you want set edges and a slightly soft center).
- Remove pan from oven. Immediately scatter chopped milk chocolate over the hot brownies.
- Sprinkle mini marshmallows evenly over the chocolate.
- Finish with graham cracker pieces on top.
- Return to oven 3-8 minutes just to puff marshmallows and soften chocolate.
- Optional: Broil 10-45 seconds to toast (watch nonstop).
- Cool at least 20-30 minutes before slicing.
Notes
- Add toppings near the end so marshmallows don't burn before brownies finish baking.
- For crunchier graham topping, use larger pieces and scatter some on after baking.
- Glass pans often need a little more bake time; start checking early either way to avoid overbaking.
- For clean slices, cool longer and wipe knife between cuts.
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