Lemon Caramel Custard

 In a small heavy saucepan, combine 3/4ths cup of the sugar, the cream of  tartar, and 1/4 cup of water; bring the mixture to a boil, stirring until  the sugar is dissolved, and boil the syrup, covered, for 1 minute.
Remove  the lid and boil the syrup, undisturbed until it begins to turn golden.  Combine to boil the syrup, swirling it and tilting the pan occasionally,  until it is a deep golden caramel. Pour the caramel into a loaf pan, 9  1/4th by 5 1/4th by 3 inches, tilt the pan to coat the bottom and
sides  with the caramel, and let the caramel cool. In a large saucepan scald the milk with the cream over moderate heat. In a large heatproof bowl whisk together the whole eggs, the egg yolks and the remaining 3/4ths cup sugar until the mixture is light and frothy. Add the scalded milk mixture in
a  slow steam, stirring constantly, and stir in the lemon juice, the zest, and the vanilla. Set the loaf pan in a larger and deeper baking pan and strain the custard mixture into the loaf pan. Cover the loaf pan with heavy duty foil and add enough hot water to the larger pan to reach two thirds of
the way up the sides of the loaf pan. Bake the custard in the middle of a preheated 325F oven for about 1 1/2 hours until a knife inserted in the middle comes out clean.  Do not overcook (The custard may  not appear set  in the middle but it will continue to cook as it cools.) Let the custard 
 cool and chill it, covered, overnight.   Servings: 10.