Line an 8- or 9-inch square baking pan with nonstick aluminum foil, or with heavy-duty aluminum foil, and grease the foil with cooking oil spray. Set the prepared pan aside.
In a medium-size, heavy-bottom saucepan, place the butter over medium-low heat until just melted. Melt it slowly and keep the heat low so the butter doesn’t brown at all.
Add the miniature marshmallows and mix to coat the marshmallows in the melted butter. Cook over medium-low to low heat, stirring frequently, just until the marshmallows are fully melted. Do not continue to cook the marshmallows once they’re fully melted or your treats will be hard.
Remove the pan of melted marshmallows from the heat, and stir in the salt and vanilla. Allow the marshmallow mixture to sit for 5 to 7 minutes, stirring occasionally, or until the mixture is no longer too hot to touch.
In a large mixing bowl, place the cereal. Pour the melted and slightly cooled marshmallow mixture on top.
Use a silicone spatula to turn the cereal over and into the marshmallow mixture, continually scooping from the bottom to moisten all of the cereal.
Transfer the mixture to the prepared baking pan, and press the mixture gently into an even layer with a greased spatula or spoon.
For a smooth top, you can also place a piece of parchment paper on top of the mixture in the pan and smooth the mixture by placing gentle, even pressure with your palms. Don’t pack the mixture down firmly in the pan.
Allow the mixture to cool, uncovered in the pan, completely to room temperature.
Remove the treats from the pan with the liner, and turn them over onto a large piece of parchment paper. Carefully peel away the aluminum foil on the bottom.
Place another piece of parchment paper on the treats, and invert them again onto a flat surface. Peel away the first piece of parchment paper. Use a large sharp knife to slice the treats into 16 equal square pieces.
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Notes
Variation of gluten free rice krispie treats made with homemade marshmallows:
2 tablespoons (14 g) unflavored powdered gelatin (if using packets, you’ll need 2)
1 cup (8 fluid ounces) cool water
2 cups (400 g) granulated sugar
⅛ teaspoon cream of tartar
1 teaspoon pure vanilla extract
⅛ teaspoon kosher salt
5 tablespoons (70 g) unsalted butter, melted and cooled
8 cups (240 g) gluten free crisp rice cereal, plus up to 1 cup (30 g) more, as desired
Line an 8- or 9-inch square (or 9-inch x 12-inch, for smaller treats) baking dish with heavy-duty aluminum foil. Grease the foil with cooking oil spray, and set it aside. In a small bowl, place 1/2 cup (4 fluid ounces) of the water, add the gelatin, and mix to combine well. Set the bowl aside and allow the gelatin to swell as it stands. Once the gelatin has swelled, transfer it to the bowl of a stand mixer (or a large bowl to use with a hand mixer). In a medium, heavy-bottom saucepan, place the remaining 1/2 cup water, sugar and cream of tartar, and whisk to combine well.Cook the sugar mixture over medium-high heat until it reaches the softball stage, between 238°F and 240°F, on an instant read thermometer.Remove the saucepan from the heat immediately, and pour the cooked sugar mixture down the side of the bowl of the stand mixer into the gelatin mixture.Whisk to combine and allow the mixture to cool briefly. It will bubble.Add the vanilla and salt, and beat the mixture on medium-high speed with the whisk attachment (or with a hand mixer) until the mixture is white, thick and glossy. It should nearly triple in size. It is ready when the mixture pours off the whisk (or beaters) very slowly when the attachment is raised.Add the melted butter to the marshmallows, and beat again on medium speed until combined. The marshmallows will decrease in size a bit.Place the crisp rice cereal in a large mixing bowl, and pour the marshmallow and butter mixture on top. Spray a silicone spatula with cooking oil spray, and use it to stir together gently the marshmallow mixture and the rice cereal. Add up to 1 cup (30 g) more crisp rice cereal if you would like your treats less gooey.Scrape the mixture into the prepared pan, and smooth the top with the oiled spatula. Do not press the mixture too firmly into the pan. Allow the mixture to cool, uncovered in the pan, completely to room temperature.Remove the treats from the pan with the liner, and turn them over onto a large piece of parchment paper. Carefully peel away the aluminum foil on the bottom.Place another piece of parchment paper on the treats, and invert them again onto a flat surface. Peel away the first piece of parchment paper. Use a large sharp knife to slice the treats into 16 equal square pieces.About the nutrition information.Nutrition information is approximate per treat for the main version above made with packaged marshmallows, is approximate and calculated with an online nutrition calculator. It is inherently unreliable.