5 tablespoons (70 g) unsalted butter, chopped
6 ounces marshmallow creme/fluff
1/8 teaspoon kosher salt
5 cups (150 g) gluten free crisp rice cereal
1/2 cup mini marshmallows (optional)
Line an 8-inch square pan with foil and spray with cooking oil spray. Set the pan aside.
Place the butter and the marshmallow fluff in a large microwave-safe bowl, and microwave for 30 seconds at high power. Stir, and microwave again for 30 seconds at a time stirring in between until just melted. Alternatively, place both in a medium, heavy-bottom saucepan and melt over medium heat, stirring frequently until just melted. Remove from the microwave, and allow to cool briefly until the mixture is no longer hot to the touch (otherwise, the crisp rice layer may taste as if it is stale, even if the cereal is fresh). If you melted the mixture on the stovetop, transfer it to a large, heat-safe bowl. Add the salt, and mix to combine.
Add the crisp rice cereal and stir gently to coat the rice cereal completely in the marshmallow mixture without crushing the cereal. Add the optional miniature marshmallows and stir gently until they’re evenly distributed throughout. Transfer the mixture to the prepared pan and press firmly into an even layer. Cover the bars with plastic wrap and allow them to sit in the pan at room temperature until set (about an hour). Remove from the pan, place on a cutting board and, using a large sharp knife and a swift motion, slice into 9 or 12 squares before serving. For the cleanest lines when cutting, place the pan in the freezer for about 10 minutes before slicing.