These peanut butter marshmallow squares are a no bake bar made with 5 ingredients: butterscotch chips, smooth peanut butter, butter, vanilla and mini rainbow marshmallows. You melt the base in one saucepan, let it cool for 8 to 10 minutes, fold in the marshmallows, then chill the pan for 1 to 2 hours and cut 16 squares.
That short cool down is the whole trick. Add the marshmallows to a hot base and they melt into pastel streaks. Wait until the pan feels warm, not hot, and they stay whole, soft and bright in every square.
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- Butterscotch chips: 2 cups
- Smooth peanut butter: ½ cup, a regular creamy one, not natural
- Unsalted butter: ¼ cup
- Pure vanilla extract: ½ teaspoon
- Mini rainbow marshmallows: 4 cups
- Pan: 8×8 or 9×9 inch, lined with parchment
- Time: 15 minutes of work, 1 to 2 hours in the fridge
An 8×8 pan gives you taller, softer squares. A 9×9 pan spreads the same mixture thinner, so the squares are a little firmer and set sooner. Either way, use parchment rather than foil or wax paper, and leave a long overhang on two sides. Those flaps are your handles when it is time to lift the slab out. If the paper slides around while you press, clip it to the pan rim with binder clips.
Regular or Natural Peanut Butter?
Use a regular smooth peanut butter, the kind that does not separate in the jar. Natural peanut butter lets its oil float out once it is warmed with the butterscotch, and the squares set soft, a bit greasy, and hard to cut. If natural is all you have, stir the jar very well and expect a softer bar that needs the full 2 hours in the fridge. The same goes for homemade peanut butter: lovely on toast, not ideal here.
Crunchy peanut butter works if you like bits of peanut in each bite. The base is just a little less glossy.
Melting the Butterscotch Base Low and Slow
Put the butterscotch chips, peanut butter and butter in a medium saucepan over low heat. Stir the whole time. In a few minutes it turns smooth and glossy, and that is the moment to take it off the heat. It does not need to bubble.
I once let it simmer, and the squares came out greasy with a dull finish. Butterscotch chips that keep cooking go thick, matte and slightly grainy. Seeing that? Pull the pan off the heat right away and stir in another spoonful of peanut butter until it loosens.
How Warm Is Too Warm for the Marshmallows?
Let the base sit off the heat for 8 to 10 minutes. It should still pour easily but no longer feel hot. I touch the side of the pan with a knuckle: when it feels like warm bathwater, stir in the vanilla.
Now tip in all 4 cups of marshmallows and fold with a silicone spatula in slow, wide strokes. You are coating them, not mixing them in. Use fresh, soft mini marshmallows. A bag that sat open in the pantry gives dry, clumped pieces and a lumpy slab with patchy color, and regular size marshmallows are too big to spread evenly.
Pressing, Chilling and Cutting 16 Squares
Spoon the mixture into the lined pan and push it into the corners with the back of a spoon or an offset spatula. Press lightly. Packing it down crushes the marshmallows and gives you a dense bar instead of a soft, chewy one.
Chill for 1 to 2 hours, until the slab is firm all the way through when you press the center. A warm kitchen needs the full 2 hours. Lift it out by the parchment, then cut a 4 by 4 grid with a long sharp knife. Dip the blade in hot water and wipe it dry between cuts, and the edges stay neat instead of smeared. They are rich, so 16 small squares go a long way.
If Your Squares Did Not Turn Out
- Marshmallows melted into streaks: the base was still hot. Next time wait the full 8 to 10 minutes and do the knuckle test.
- Soft in the middle after chilling: natural peanut butter or too short a chill. Give it another hour in the fridge, or 20 minutes in the freezer.
- Greasy or dull top: the base simmered. Keep the heat low and stop as soon as it is smooth.
- Squares crack when cut: the slab is too cold, often straight from the freezer. Let it stand 10 minutes, then cut.
Storing Marshmallow Squares at Room Temperature or Cold
They hold their shape at room temperature for a party table or a bake sale, but I like them slightly chilled. For keeping, store them in an airtight container in the fridge for up to a week, with parchment between layers. To freeze, wrap each square tightly and thaw it in the fridge before serving.
Confetti Squares, Chocolate Versions and Other Swaps
In Canada, many people know these as confetti squares, and the method is the same. For chocolate peanut butter marshmallow squares, swap the 2 cups of butterscotch chips for 2 cups of semisweet chocolate chips. Want a base under the marshmallows? My butterscotch marshmallow squares sit on a pressed graham crust.
For more peanut butter and marshmallow, peanut butter Rice Krispie treats and peanut butter s’mores bars are close cousins. For another no bake pan, try no bake peanut butter bars, peanut butter fudge or peanut butter no bake cookies. For a birthday, the Reese’s peanut butter cake is the bigger project.
Quick Questions About These Squares
Can I use large marshmallows?
Mini marshmallows work best. Large ones are too bulky to spread evenly through the base, so the squares cut unevenly.
How long do peanut butter marshmallow squares take to set?
Plan on 1 to 2 hours in the fridge. They are ready when the center feels firm under a fingertip.
Why did my marshmallows melt?
The peanut butter base was too hot. Let it cool for 8 to 10 minutes off the heat until it feels warm, not hot.
Made a batch? Leave a comment below and tell me which pan size you used.
Peanut Butter Marshmallow Squares
These peanut butter marshmallow squares are a no bake bar made with butterscotch chips, smooth peanut butter, butter, vanilla and mini rainbow marshmallows. One 8x8 or 9x9 inch pan takes 15 minutes of work and 1 to 2 hours in the fridge, then cuts into 16 soft, chewy squares. The key step is letting the melted butterscotch base cool for 8 to 10 minutes, so the marshmallows stay whole and colorful instead of melting. Many Canadian bakers call them confetti squares, and they suit bake sales, potlucks, school lunches and holiday cookie trays. For chocolate peanut butter marshmallow squares, use semisweet chips; keep them in the fridge for up to a week.
Ingredients
- 2 cups butterscotch chips
- 1/2 cup smooth peanut butter (not natural)
- 1/4 cup unsalted butter
- 1/2 teaspoon pure vanilla extract
- 4 cups mini rainbow marshmallows
Instructions
- PREPARE THE PAN: Line an 8x8-inch or 9x9-inch square baking pan with parchment paper, allowing extra on the sides to lift the bars out easily once set.
- MELT THE BASE MIXTURE: In a medium saucepan over low heat, combine the butterscotch chips, peanut butter, and butter. Stir constantly until the mixture is completely melted and smooth. Remove from heat as soon as the mixture is uniform and glossy.
- COOL SLIGHTLY: Allow the mixture to cool for 8 to 10 minutes. It should remain pourable but not be hot to the touch. This prevents the marshmallows from melting when added.
- ADD VANILLA AND MARSHMALLOWS: Stir in the vanilla extract. Gently fold in the mini rainbow marshmallows using a spatula, being careful not to crush them.
- PRESS INTO PAN: Transfer the mixture to the prepared pan. Press it evenly into the pan with a spatula or the back of a spoon, spreading it to the corners without compressing the marshmallows too much.
- CHILL AND SET: Refrigerate the pan for 1 to 2 hours until the bars are firm and set all the way through.
- CUT AND SERVE: Lift the set mixture out of the pan using the parchment overhang. Use a sharp knife to cut into 16 squares, cleaning the knife between cuts for neat edges.
Notes
Use regular smooth peanut butter, not natural; natural peanut butter separates and the squares set soft and greasy. Take the base off the heat as soon as it is smooth and glossy; if it simmers it turns thick and dull. Wait 8 to 10 minutes before adding the marshmallows, until the pan feels warm, not hot. Use fresh mini marshmallows; regular-sized marshmallows are too bulky and will not distribute evenly. Cut with a knife dipped in hot water and wiped dry. Store in an airtight container in the fridge for up to 1 week, or wrap and freeze, then thaw in the fridge.
Nutrition Information
Yield
24Serving Size
1Amount Per Serving Calories 152Total Fat 9gSaturated Fat 5gTrans Fat 0gUnsaturated Fat 3gCholesterol 5mgSodium 45mgCarbohydrates 18gFiber 0gSugar 15gProtein 2g
