Lightly grease a 13×9” (33x23cm) baking dish with butter and set aside.

Brown the butter: Place butter in a large pot and heat over medium-low heat until melted. Once melted, increase heat to medium (or just a notch above medium) and cook the butter, swirling and stirring as it begins to bubble and pop. Once the bubbling and popping slows down you will notice brown bits forming on the bottom of the pan – congratulations, your butter is browned!

Once butter is browned, turn heat to low and add marshmallows and vanilla extract, stirring gently until marshmallows are just melted.

Remove pot from heat and cereal. Stir gently until cereal is evenly coated.

Spread into prepared pan and cool 5-10 minutes before sprinkling with sea salt. Allow to cool completely before cutting and serving.