Steps
- Butter an 8in / 20cm square pan with 2in / 5cm sides.
- Melt ½ cup of unsalted butter in a large pot over medium-low heat. Stir frequently until it turns nut brown and smells toasted.
- Turn off the heat and stir in 285g of marshmallows until smooth, returning briefly to low heat if needed.
- Off the heat, stir in ¼ teaspoon of coarse sea salt and 6 cups of crispy rice cereal. Press evenly into the pan with greased parchment. Cool, then cut into squares.