These Disappearing Marshmallow Brownies are full of chocolate chips and a have pockets of melted marshmallows scattered throughout, making these bars chewy and irresistible!!

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A piece of disappearing marshmallow brownies being scooped out of a pan.

This Disappearing Marshmallow Brownies recipe is one that my mom has been making since I can remember. It came from an old church cookbook - one that's now looking....well, very "well-loved." These cookie bars are chocolate-y and the best chewy texture, thanks to those "disappearing marshmallows!"

How do you make Disappearing Marshmallow Brownies?

First, you’ll prepare your pan by either lining with parchment paper or giving it a layer of cooking spray. Then, you’ll melt the butter and butterscotch chips using either the microwave or a saucepan. Once the butterscotch mixture has cooled a bit, you’ll stir in the flour, brown sugar, baking powder, salt, eggs and vanilla. Once that’s smooth, you’ll gently stir in the marshmallows, chocolate chips and chopped nuts (which are optional). Next, you’ll spread the batter into your pan, bake, cool, cut and enjoy!!

Two disappearing marshmallow brownies stacked on top of each other.

Should I grease the pan or use parchment paper when making cookie bars?

It depends….. Here’s what I ask myself when deciding:

Do the bars have caramel bits, a sticky sauce or marshmallows in the batter?
Is it important for the bars to have nicely cut, clean lines? (for example, you’re taking them to a party, etc)

If the answer to either of these is YES, I’d highly recommend parchment paper. Here’s why. First off, you don’t have to worry about the bars sticking to the bottom of the pan. Secondly, being able to take the bars out of the pan in one large chunk makes it easy to cut perfect, clean-edged bars. More on that to come below…

A stack of brownies with the top one pulled apart showing strings of marshmallow.

Here’s how to line a pan with parchment paper:

Spray the pan with cooking spray so the parchment doesn’t move around when the batter goes in
Cut the parchment paper to the size I need. You’ll want to make sure the bottom of the pan is covered and that there’s a little extra paper to use as “handles” when pulling the bars out of the pan
Add the batter and spread it out, carefully, so the paper stays in place
Bake the bars
Remove the bars from the oven and run a butter knife around the edges just in case it’s sticking to the edges of the pan
Let the bars cool completely. You can let them cool on the counter at room temperature, but if you’re a little more impatient (like myself), you can also stick them in the fridge
Once they’re cool, you’ll be able to pull the bars out of the pan, transfer to a large cutting board, remove the parchment paper and cut the bars into nice clean squares!

A stack of four disappearing marshmallow brownies surrounded by other ingredients.

How do I know when the Disappearing Marshmallow Brownies are done baking?

You’ll bake these for 20-25 minutes, but as you know, ovens can vary quite a bit. Therefore, it’s nice to have an idea of what they should look like when finished. When these Disappearing Marshmallow Brownies are ready to come out of the oven, they’ll be golden brown on top and the bars will be a little jiggly. Don’t worry too much about the jiggle, as they’ll firm up once they’re cool.

But for future reference, any cookie, bar, brownie, cake, etc, is safe to eat once the very center is 160F or warmer (as this is the temperature that eggs are fully cooked). If you don’t have a thermometer you love and trust, I’d highly recommend this one or this one!! Such a helpful product to have.

A piece of disappearing marshmallow brownies.

Where do the marshmallows “disappear” to?

Although these bars taste quite magical, the marshmallows don’t really “go” anywhere. Essentially, when the brownies (or I really should call them blondies!) are baking, the marshmallows melt, forming marshmallow-lined holes that make these brownies so, so tasty!!

A couple pieces of disappearing marshmallow brownies arranged in a pan.

Some of my other favorite cookie bars...

If you're looking for something super quick and no-bake, the Best Ever Scotcheroos are my go-to, with these No Bake S'mores Bars being a close second!!

If you're a peanut butter fan, these Peanut Butter Bars are just to die for! And Oh Henry Bars are also super delicious!!!

And if you are a fan of nuts, these Butterscotch Brickle Bars might just be my #1 favorite bar recipe out there!! They're so crunchy, flavorful and....addictive!