Salted Caramel Sauce

1/2 C unsalted butter cubed
1 C brown sugar packed
1/4 C ilk
1 tsp vanilla extract
1/4 tsp kosher salt or sea salt or to taste

Place butter in a saucepan and melt over medium-low heat. Add the brown sugar and milk and turn heat to medium. Stir constantly until the mixture boils. Boil for two minutes. Remove from heat and stir in vanilla and salt. (Once it cools a bit, you can add more salt to taste.) Pour into jar. Let cool slightly before using. Cover. Store in refrigerator if not using the day it's made. If mixture separates as it cools, just stir it up or shake it. If it becomes too thick to pour after chilling, you can heat it in the microwave for a few seconds and stir.