In a large pot, melt butter over medium heat. Keep stirring it as it melts.

Continue cooking the butter, stirring constantly. It will start to foam, and then you'll see brown specks forming at the bottom of the pot. When it turns a nice golden brown color and has a nutty aroma, it's ready. This takes about 5-7 minutes.

Add the mini marshmallows to the pot with the browned butter. Stir constantly until the marshmallows are completely melted and smooth.

Stir in the vanilla extract and sea salt until well combined.
Remove the pot from heat and immediately add the Rice Krispies cereal. Stir until all the cereal is evenly coated with the marshmallow mixture.

Lightly grease a 9x9-inch baking dish with butter or non-stick spray.

Add the mixture into the prepared pan. Use a spatula (or your hands lightly greased with butter) to press the mixture evenly into the pan. Do not press too hard.

Let the Rice Krispie squares cool completely in the pan. This usually takes about 30 minutes.

Once cool, cut into squares and serve. Enjoy!