In a medium saucepan, melt the butter over medium heat. Continue to cook the butter, stirring frequently, until it turns a golden brown and has a nutty aroma, about 5-7 minutes. Be careful not to burn it!
Once browned, remove the saucepan from the heat and stir in the sea salt and vanilla extract.
Immediately add the large marshmallows and mini marshmallows to the saucepan. Stir until the marshmallows are completely melted and combined with the brown butter.
Gently fold in the Rice Krispies cereal until evenly coated with the marshmallow mixture. If using chocolate chips or sprinkles, add them now and mix briefly to combine.
Grease a 9x13 inch baking dish with cooking spray or butter. Pour the mixture into the dish and press it down evenly with a spatula or your greased hands. Be careful not to press too hard!
Allow the treats to cool at room temperature for about 30 minutes before cutting them into squares or rectangles.
Notes
Serve in a fun dish or wrap individually for sharing.
Keyword Brown Butter, dessert, Rice Krispie Treats