INGREDIENTS
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8 tablespoons (115 grams or 1 stick) unsalted butter, plus more for the pan
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Heaping ¼ teaspoon flaky sea salt
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One 10- ounce (285-gram) bag large or miniature marshmallows
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6 cups (170 grams) puffed- rice cereal (about half a 12- ounce box; I've had luck with brown rice cereals as well)
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Butter (or coat with nonstick spray) an 8- inch square cake pan with 2-inch sides