1cansweetened condensed milk, add only ½ to begin with
1 ½cupschopped toasted pecans, optional
Butter the sides and bottom of a 9X13-inch pan. Set aside.
In a medium heavy saucepan, add sugar, corn syrup, 1/2 can sweetened condensed milk, salt and butter.
Over medium-low heat, stirring constantly to ensure the sugar is completely melted, bring the mixture to a boil and add the rest of the sweetened condensed milk when it begins to boil.
Insert the candy thermometer and clip onto your pan at this point. Once the second half of the condensed milk has been added and the mixture is boiling again, stop stirring to prevent sugar crystallization (which means the caramels will have a grainy texture). Boil the mixture still at medium-low heat, without stirring until the mixture reaches the soft ball stage on a candy thermometer (234 degrees F). If you like your caramels a bit firmer, you can cook them up to 248 degrees F, which is firm ball stage but I prefer mine really soft (I will warn you that most people find this stage a bit too soft so use your best judgment and preference).
When the caramel reaches the right temperature, immediately remove the pan from the heat and stir in the vanilla and toasted pecans (if using).
Carefully pour the hot mixture into the prepared pan without scraping the bottom and sides of the pan. Let the caramel cool completely before cutting into squares and wrapping in waxed paper.