Combine brown sugar, sugar, corn syrup, butter, and evaporated milk in a heavy saucepan. Bring to a boil over medium heat.
Boil, stirring constantly, for 15-20 minutes or till mixture thickens. I like mine pretty thick (almost to a soft ball stage if you want to use a thermometer). Remove from heat and stir in vanilla and salt.
Sauce will thicken as it cools. Serve warm over ice cream.
Notes
Makes about 2 1/2 cups of caramel sauce.
If your heat is set too high, the sauce may appear curdled. If this happens, just let it cool a little, then pour it into a blender and blend till smooth. Works like a charm.