Peanut butter marshmallow squares are a no-bake bar made from a smooth butterscotch-peanut butter base and colorful mini marshmallows. Five ingredients and one saucepan produce a soft, chewy treat that sets in the refrigerator, so the recipe is useful when oven space is limited or a dessert needs to be prepared ahead.
The key is temperature control rather than baking. The peanut butter mixture must melt gently enough to remain smooth, then cool for two to three minutes before it touches the marshmallows. That brief pause keeps the marshmallows distinct instead of dissolving into the hot base. A full chill gives the slab clean edges and makes sixteen tidy squares.
Ingredients for Peanut Butter Marshmallow Squares
The base uses one-half cup unsalted butter, one cup creamy peanut butter, one 11-ounce bag butterscotch chips, and one teaspoon vanilla extract. Regular commercial creamy peanut butter gives the most dependable set because the oil remains evenly emulsified. Natural peanut butter that separates can leave the bars greasy or unusually soft.
Add one 10-ounce bag fruity-flavored mini marshmallows after the melted mixture has cooled briefly. Regular white mini marshmallows can be used with the same method, although the appearance and fruit flavor will change. Light cooking spray and parchment paper prepare an 8-by-8-inch pan.
If you enjoy this recipe, you may also like Peanut Butter Snickers Cheesecake.
How to Make the Squares
- Prepare the pan. Line an 8-by-8-inch pan with parchment, leaving overhang on two sides, and coat it lightly with nonstick spray.
- Melt the base. Combine butter, peanut butter, and butterscotch chips in a medium saucepan over medium-low heat. Stir constantly until smooth.
- Add vanilla and cool. Remove the pan from the heat, stir in vanilla, and let the mixture stand for two to three minutes.
- Fold with marshmallows. Put the mini marshmallows in a large bowl. Pour the warm base over them and fold gently until evenly coated.
- Fill the pan. Transfer immediately and spread into an even layer, pressing only enough to remove large gaps.
- Chill. Refrigerate for one and one-half to two hours, until firm through the center.
- Cut. Lift out the slab and divide it into sixteen squares with a large sharp knife, warming and wiping the blade between cuts.
For storage details after serving, the USDA leftovers and food safety guidance.
Line the Pan for Easy Removal
Fit parchment across the bottom and up two opposite sides of the 8-by-8-inch pan. Leave enough paper above the rim to act as handles after chilling. A very light layer of cooking spray keeps the sticky mixture from gripping the parchment and corners.
Prepare the pan before melting anything. Once marshmallows are folded into the base, the mixture thickens as it cools and should be transferred promptly. Searching for parchment at that stage leads to uneven bars and unnecessary handling.
If you enjoy this recipe, you may also like Cranberry Pistachio Shortbread Cookies.
Melt the Base Slowly
Place the butter, creamy peanut butter, and butterscotch chips in a medium saucepan over medium-low heat. Stir across the bottom and into the corners with a flexible heatproof spatula. Gentle heat allows the chips to melt into the fats without scorching or becoming grainy.
Do not wait for the mixture to boil. Remove it from the burner as soon as it looks glossy and no whole chips remain. If the pan becomes very hot or the base begins sticking, lower the heat immediately. Butterscotch chips contain sugar and can burn against the metal before the entire mixture appears damaged.
Cool Before Adding Marshmallows
Stir in the vanilla after taking the saucepan off the heat. Let the mixture stand for two to three minutes, stirring once or twice to release heat evenly. It should remain fluid enough to coat the marshmallows but should no longer be steaming aggressively.
This pause is central to the recipe. If the base is poured straight from a very hot pan, the mini marshmallows soften, smear, and lose their individual colors and shapes. Waiting too long creates the opposite problem: a thick base that cannot coat them evenly. Warm and pourable is the target.
Fold Gently but Thoroughly
Place the full 10-ounce bag of mini marshmallows in a roomy mixing bowl. Pour the slightly cooled base over them in a broad stream, then lift and fold from the bottom with a spatula. Turn the bowl as you work so dry pockets do not remain.
Avoid vigorous stirring, which can crush the marshmallows and introduce smears of color into the base. Stop when every marshmallow has a thin coating and the mixture looks evenly distributed. Transfer it to the prepared pan immediately while it is still flexible.
Press Without Compacting
Spread the mixture toward each corner with the spatula. Press gently to create a level surface and eliminate obvious empty spaces, but do not compress it as firmly as a cereal bar. Heavy pressure flattens the marshmallows and removes the soft, pillowy texture that distinguishes these squares.
If the spatula sticks, coat it very lightly with nonstick spray or cover the surface with a loose piece of parchment while pressing. Keep the final thickness even so the center and edges become firm at the same rate in the refrigerator.
Chill for a Clean Set
Refrigerate the pan for at least one and one-half hours and allow up to two hours for a firm center. The surface may feel set before the middle is ready, so avoid lifting and cutting too soon. Proper chilling keeps the squares from bending or smearing under the knife.
Once firm, use the parchment handles to raise the whole slab onto a cutting board. If it resists, loosen the two unlined sides with a thin spatula. Do not pull one parchment handle sharply, which can crack an overly cold slab.
Cut Sixteen Even Squares
First divide the slab into four equal strips, then cut each strip into four pieces. A large, straight-edged knife produces cleaner lines than a small serrated blade. Run the knife under hot water, dry it completely, and wipe it after each long cut.
The warm blade passes through the peanut butter base without dragging marshmallows across the surface. Drying is important because drops of water create wet marks and shorten storage life. Let very cold bars stand for a few minutes if they feel brittle.
Serving and Variations
Serve the squares slightly chilled or let them stand briefly for a softer texture. Because peanut butter and butterscotch are rich, sixteen modest pieces are more practical than oversized bars. Clearly identify the peanut content when sharing them at a gathering or packing them for others.
White mini marshmallows can replace fruity ones without changing the method. Chocolate chips may replace the butterscotch chips for a chocolate-peanut butter version, although the flavor and firmness may differ. Any substitute chips should be melted with the same gentle heat.
Storage and Food-Safety Notes
Arrange the squares in an airtight container with parchment between layers and refrigerate for up to one week. Keeping them covered prevents the marshmallows from drying out and protects the bars from refrigerator odors. For serving, take out only the amount needed and return the rest to the refrigerator.
These bars contain peanuts and commonly contain milk and soy through the butter, peanut butter, and chips. Marshmallow ingredients can also vary, so check every label when preparing them for dietary needs. Freezing is not ideal because thawed marshmallows can become sticky and lose their best texture.
Conclusion
Melt butter, creamy peanut butter, and butterscotch chips over medium-low heat, stirring until smooth. Add vanilla off heat and cool for two to three minutes before gently folding the mixture into mini marshmallows. Press into a lined 8-by-8-inch pan, chill for one and one-half to two hours, and cut into sixteen squares with a warm, clean knife.
Frequently Asked Questions
- → Why did my marshmallows melt into the base?
The peanut butter mixture was too hot. Let it cool for two to three minutes off heat before pouring it over the marshmallows.
- → Can natural peanut butter be used?
Regular stabilized creamy peanut butter gives the most reliable set. Separated natural peanut butter can make the bars oily or too soft.
- → How long should the squares chill?
Refrigerate them for one and one-half to two hours, until the center is firm enough to lift and cut without bending.
- → How should peanut butter marshmallow squares be stored?
Keep them in an airtight container in the refrigerator for up to one week, with parchment between layers.