In a small double boiler bowl, whisk together ½ cup of the sugar, egg yolks, lemon juice, and salt. Fill a double boiler pot with one inch of water. Make sure the water doesn’t touch the bowl when the bowl is inserted in the pot, and turn to medium heat. Place bowl in pot, and whisk constantly. As the mixture starts to thin, whisk in other ½ cup sugar. Whisk and cook until very hot, almost ready to boil, but not boiling. Remove from heat, and stir in lemon zest. Allow to cool completely.

In 4 cup measure or large bowl, combine milk, half and half, cream and vanilla. Whisk in cooled lemon curd. Cover and refrigerate at least 2 hours.