Dissolve the rock candy in hot tea and allow to cool.
Bring the milk to a boil. Mix the cornstarch with the egg yolk and cold tea. Pour the mixture into the boiling milk and bring to the boil briefly. Beat the egg white until stiff and fold into the tea cream together with the rum.
In the meantime, whip the cream until stiff. Let the cream cool in the refrigerator and serve garnished with cream.