Add cream, milk, sugar, salt and 1 cup peanut butter to a saucepan over medium heat. Stir constantly until the sugar dissolves and the peanut butter melts, making sure not to let it stick to the bottom. Continue to heat until the mixture becomes warm and begins to bubble around the edges. Remove from heat, add in vanilla extract and add the mixture to a bowl and refrigerate until cold, at least 30 to 60 minutes.