Toffee-Caramel Sauce

This recipe comes (with some changes) from food.com. Thanks to ElaineM. I made this sauce for an apple cake. It's really good!

1/2 c butter
1/2 c brown sugar, packed
1/4 c white granulated sugar
1-1/2 T water
pinch of salt
1/2 c evaporated milk
2 t vanilla extract

Heat the butter, sugars, water, and salt in a pan over medium heat. Stir constantly, and after it begins to boil, cook for another 3 - 5 minutes. The longer it cooks, the thicker the sauce. Remove the pan from the heat, and stir in the milk and vanilla. The sauce will thicken as it cools.