Grease the sides of a medium saucepan with oil or non-stick spray. Add butter, brown sugar, water, and salt to saucepan and cook over medium-low heat, stirring constantly, until the butter has melted.

Bring the mixture to a boil., stirring constantly. Reduce heat to a simmer and cook for 5-8 minutes, stirring, until golden brown and thickened (keep in mind it will continue to thicken as it cools).

Remove from heat and stir in vanilla and 1/2 cup evaporated milk. Add more evaporated milk if you'd like a thinner consistency.

Store caramel sauce in a covered container or jar in the refrigerator for 1-2 weeks. Re-warm in the microwave for a few seconds, or on the stove over low heat.