To make the caramel, combine butter, brown sugar, condensed milk, corn syrup and salt in a heavy saucepan.

Bring it to a boil over a high heat, stirring constantly until the mixture reaches 240 degrees F on a candy thermometer.
Remove from the heat and stir in the vanilla.

Pour into a well greased 8 x 8 pan, and let set overnight at room temperature or for a few hours in the fridge.

Remove caramel from the pan and cut into small cubes with a sharp knife. Wrap in parchment paper squares. Or, add salt first for salted caramels. Or, dip in chocolate and then sprinkle with salt for chocolate salted caramels.