Combine brown sugar, half and half, butter and salt in a small saucepan over medium heat. Bring to a simmer while stirring constantly then turn heat down slightly and continue simmering while stirring until mixture has thickened, 10-12 minutes. Remove pan from heat then stir in vanilla and set aside to cool completely. Can be made up to 5 days ahead of time.
For the Dip:
Reserve 2 Tablespoons caramel sauce for topping the dip with then add 1 cup caramel sauce to a large mixing bowl with the cream cheese and whisk until smooth. Add whipped topping then fold with a spatula to combine. Refrigerate dip until completely chilled, at least 2 hours.
Scoop dip into a serving bowl then top with reserved caramel sauce and crushed graham crackers (optional) then serve with apple slices and graham crackers.