In a saucepan, whisk together the cream, milk, cinnamon, salt, and the remaining sugar over medium-high heat. When the mixture just approaches a simmer, reduce the heat to medium. Next, scoop out 1/2 cup of the hot cream mixture and, while whisking, add the cream to the bowl with the egg and sugar mixture. Repeat this step once more with another 1/2 cup of hot cream mixture. Now that the egg mixture has been tempered, slowly pour the egg and cream mixture into back into the saucepan, stirring constantly.