Add the cream, milk, sugar, pumpkin puree, vanilla extract, pie spice and salt to a saucepan over medium heat. Stir constantly until the sugar dissolves and the mixture is combined, 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 the mixture to a bowl and refrigerate until cold, at least 30 to 60 minutes.