Lightly butter a square pan. Have a rubber spatula and a medium pot ready.

Melt butter in a pot, then stir in caramel sauce and salt until smooth. Remove from heat and stir in vanilla.

Add marshmallows to the caramel mixture, stirring until half-melted; then return to low heat briefly.

Pour the marshmallow mixture over the Rice Krispies in a bowl. Toss until coated.

Scrape the mixture into the pan. Press gently and evenly.

Let it rest, then chill in the fridge. Slice into squares.