Line a baking pan with parchment paper or waxed paper; set aside.
In a large pot, melt butter over medium-low heat. It will melt, foam, then turn golden brown and smell nutty. Watch carefully, stirring constantly.
When butter is evenly browned, stir in marshmallows, salt and vanilla. Cook, stirring often, until mixture is melted and smooth, 3 to 5 minutes. If using, stir in your caramel sauce now. Remove pot from heat.
Stir in crispy rice cereal and mix well, preferably with a silicone spatula. Scrape into prepared pan and press down lightly (easy tip: coat your spatula or hands with butter or cooking spray, then press down on cereal mixture - this helps avoid a sticky mess). Dust top with additional salt, if desired.
Let treats cool at least 15 minutes in your refrigerator. Cut into squares or bars.