Combine 1 quart of the milk in a saucepan with the sugar, and cook over a low heat, stirring from time to time, until the mixture turns golden.
Meanwhile, stir the soda into the remaining quart of milk in a saucepan.
Add the cinnamon stick, and bring to a boil.
Discard the cinnamon.
Add the hot milk to the caramel mixture very gradually, stirring constantly.
When all the milk in incorporated, place over a low heat, and cook very slowly until the mixture is thick.
Cool slightly; then pour into a glass serving bowl, and chill.