In a saucepan over medium heat, melt brown sugar and butter together. Bring to a boil and remove from heat.
Whisk in evaporated milk, vanilla, and salt. Use immediately or store covered in the refrigerator for one month. Yield: About 2 cups.
Salted caramel: Add more salt to taste for your very own salted caramel sauce (start with 1/4 teaspoon salt and add more to taste, a little bit at a time).
The sauce thickens as it cools: Pour it into a glass jar or another easily-accessible container and cover tightly! In the fridge, it thickens up even more. It can get gritty when eaten cold straight out of the jar but reheats beautifully.
Candy coating: This is not the right caramel for dipping apples or making candies.
Make ahead: Refrigerate for up to two weeks, then microwave or reheat over low heat on the stove.
Freezing and reheating: Stored in an airtight container, caramel sauce keeps for up to 3 months in the freezer. Thaw it overnight in the refrigerator before reheating gently on the stove.