In a large pot, melt butter over medium to medium-low heat. It will melt, then foam, then turn clear golden and finally start to turn brown and smell nutty. Add sea salt. Stir frequently, scraping up any bits from the bottom as you do. Don't take your eyes off the pot as while you may be impatient for it to start browning, the period between the time the butter begins to take on colour and the point where it burns is often less than a minute.
As soon as the butter takes on a nutty color, reduce heat to low and stir in the marshmallows. Continue stirring until marshmallows are melted and smooth.
Remove the pot from the stove and gently fold in the cereal, until combined. Turn the mixture onto the buttered baking sheet and press flat with your hands. As you press the mixture together, create an outside edge with a spatula.
Let cool, cut into squares and and listen up for the "Mmmm-ing".
**Adapted from Smitten Kitchen and Pioneer Woman
for The Last Wonton. Thanks oodles Deb and Ree!**