In a non-stick pot, put the sugar, cornstarch and salt. Gradually add hot water and heat on medium, stirring, till thickened. Put the yolks in a little dish and add about 3 T. of the hot mixture to them, stirring briskly. Then add the yolks back to the pot.
Cook for 5 more minutes on low heat, stirring. Whip the mixture with a mixer until light. Stir in the butter, rind, and lemon juice - chill 30 minutes.
With your mixer, combine the lemon mixture and the cream cheese until light and smooth. Pour into little "pots de creme" containers OR pour into a pretty serving dish.

Chill 4-5 hours.