In a heavy bottom sauce pan, combine the brown sugar, corn syrup, cream, salt, and butter.
Over medium-high heat stir the mixture until butter has melted and then continue to cook the mixture without any further stirring.
Use a clean pastry brush with water to wash down the sides of the pot to prevent crystalization.
Place the lid on the saucepan and let the mixture boil for 5 minutes. The condensation will also wash down the sides of the pot to prevent crystalization.
Attach your candy thermometer to the side of the pan and continue to cook the caramel until it reached 240-245ºF
Remove the caramel from the heat and stir in the vanilla, taking care not to burn yourself as the caramel will bubble up when you add it.
Let the caramel cool down for 5-10 minutes. It will be ready to dip around 190-200ºF. If your caramel is too runny, allow it to cool for 5 more minutes, it will continue to set up.
Using an oven mitt to hold your pot of caramel at an angle, gently roll your apple in the caramel until evenly coated.
Let the excess caramel drip off the bottom and gently scrap the excess on the edge of the pan before placing the apple on the silicone mat to cool.
Let the apples cool completely. Placing the apples in the fridge will speed up the cooling, however you need to wrap them after coming out of the fridge or they will condensate. Apples will last in the fridge in an airtight container for a few days.