Melt the butter in a large saucepan over medium heat.
Pour in the sweetened condensed milk, corn syrup, and add in the brown sugar.
Using a whisk or rubber spatula, stir all ingredients over medium heat until it starts to simmer. Scrape the sides and bottom regularly.
Let the sauce simmer until the temperature reaches 200-205 degrees. We want to simmer the sauce long enough to eliminate granulation, but not to reach the soft ball stage.
Once the sauce has reached the desired temperature, remove from heat and carefully stir in the vanilla and salt until everything is well combined.
Let the sauce cool, then pour it into jars for storage.
Notes
This recipe can yield about 2 to 2 1/2 cups of caramel sauce. The sauce can be served as a dip, topping, or filling for your favorite desserts. Enjoy!