Combine the heavy cream, corn syrup, brown sugar, butter, and salt in a 3-quart heavy-duty over medium heat. Do not turn the temperature up or down – Sally says to keep it at medium the entire time the caramel cooks. Stir constantly with a wooden spoon until the butter is melted.
Once melted, brush down the sides of the pan with a dampened pastry brush and attach a candy thermometer to the pan, making sure the tip does not touch the bottom of the pan, as this will render a false reading.
Without stirring, let the mixture cook and bubble until it reaches anywhere between 235⁰F to 240⁰F. This will take about 20 minutes or longer to reach this temperature, but don’t worry about the time, just focus on the temperature reading and use it as your guide. The temperature heats up slowly and then moves quickly as it gets hotter, so keep your eye on it!
Once the temp reaches 235⁰ to 240⁰F, remove the pot from the burner and carefully stir in the vanilla. Stirring too vigorously will cause air bubbles that could pop up on the coated apple!
Allow the caramel to cool for 10-15 minutes until it thickens slightly. If the caramel is too thin to cat the apples, let it cool and thicken for 5-10 more minutes before dipping the apples.
