1.Add butter, brown sugar, water, and salt to medium saucepan and heat over medium-low heat, stirring until butter melts.
2.Bring to a boil then reduce to a vigorous simmer, whisking constantly until thickened, approximately 5-7 minutes. Keep in mind, the caramel sauce will thicken more as it cools. If the caramel sauce still looks thin after you remove it from the heat, then return to a simmer.
3.Remove from heat and stir in evaporated milk (it will bubble a lot) and vanilla. Add additional evaporated milk to reach desired consistency.