Salted Brown Butter Crispy Treats

Ingredients

• 1/2 cup (4 ounces or 115 grams) unsalted butter, plus extra for the pan
• 1 10-ounce (285-gram) bag marshmallows
• heaping 1/4 teaspoon coarse sea salt
• 6 cups (160 grams) crispy rice cereal (about half a 12-ounce box)