Beat the egg yolks slightly, then add the sugar and salt. Scald the milk and slowly add to the egg mixture whisking constantly to prevent yolks from curdling. Place the custard in a double boiler (or a heat proof bowl set on top of a saucepan of simmering water) and stir until it begins to thicken and coat the back of a spoon. Remove from heat and cool slightly. Add the vanilla and lemon rind. Chill thoroughly until ready to use. This is to a firm custard but a sauce. Do not let the sauce come to a boil or it will curdle. Makes 2 1/2 cups.