Lightly grease a 9” x 13” square pan.
In a large pot, melt the butter over medium-low. Set aside the butter wrapper for later.
Once the butter is melted, continue to cook and stir constantly, until foaming and dark golden brown.
Remove from heat.
Add 4 ½ cups mini marshmallows and stir until melted.
Add Rice Krispies cereal and remaining 1 cup of mini marshmallows.
Stir to fully coat in melted marshmallow.
Transfer to pan.
Place the butter wrapper on the treats, butter side down. Very gently, apply pressure to press into the pan. Working from the center, smooth out towards the edges.
Crush sea salt as finely as possible and sprinkle evenly over the top.
Lightly cover the pan and allow treats to sit for one hour before cutting and serving.