Mix sugar and cream of tartar in medium saucepan.
Add eggs and water; beat until well blended.
Add chocolate; cook over low heat, stirring constantly, until chocolate is melted and temperature reaches 160°F. Do not allow to boil.
Cool quickly, set pan in larger pan of ice water.
Stir vigorously until temperature of mixture falls to 80°F to 90°F.
Beat butter in mixer bowl on medium speed until light and fluffy, 3 to 4 minutes.
Add cooled egg mixture; beat on high speed 4 to 5 minutes.
Refrigerate at least 6 hours before serving.
To serve, garnish with whipped cream, toasted slivered almonds and chocolate shavings.
Cream of tartar: This acidic ingredient promotes egg coagulation. Without it this pie filling might not be firm enough to slice.
Shortcut: A prepared 9-inch graham cracker crumb crust or baked pastry shell can be substituted for homemade.
Refrigerate any leftover pie promptly.
This recipe is an excellent source of choline, iron, and a good source of protein, fiber, Vitamin A and Vitamin D.