In a medium, heavy-bottomed sauce pot, combine the rest of the milk and the cream, sugar, and salt. Cook over medium heat, whisking occasionally to dissolve the sugar, just until the milk starts to boil, 2 to 3 minutes. Reduce the heat to low and immediately pour in the milk and cornstarch mixture, whisking slowly but steadily for 3 minutes more. The mixture will thicken and should have a texture similar to cake batter.