In a heavy saucepan, combine 1/2 cup apple juice and cornstarch; mix well. Add remaining juice. Place over medium heat and cook, stirring, until mixture comes to a boil. Reduce heat and simmer for 2 minutes. Remove from heat.
In a bowl, beat egg with a fork. Add 1/2 cup of hot mixture to beaten egg. Stir until smooth. Return immediately to hot mixture, stirring constantly. (The hot mixture will cook the egg.)
Stir in sweetener and cinnamon. Pour into 4 dessert dishes, cover with plastic wrap to prevent skin from forming. Cool to room temperature or chill in refrigerator.