Position rack in lower third of oven and heat to 350 degrees F. Spray sides of 8-inch round cake pan (not springform) with nonstick spray and line the bottom with parchment paper. In a kettle, bring water to boil.
Place chocolate in large bowl. Combine whole egg and 1 yolk in small bowl with vanilla. Place 2 egg whites in medium bowl with cream of tartar.
Combine the cocoa, flour and 2/3 cup sugar in a 1- to 1-1/2-quart heavy-bottom saucepan. Whisk in about half the milk to form a smooth paste. Mix in remaining milk. Cook over medium heat, stirring constantly with a wooden spoon to prevent burning (especially around the bottom edges), until mixture begins to simmer. Simmer very gently, stirring constantly, for 1-1/2 minutes. Pour hot mixture immediately over chopped chocolate. Stir until chocolate is completely melted and smooth. Whisk in egg-vanilla mixture. Set aside.
Beat egg whites and cream of tartar at medium speed until soft peaks form. Gradually sprinkle in the remaining 1/4 cup sugar, beating at high speed until stiff but not dry. Fold a quarter of the egg whites into chocolate mixture to lighten it. Fold in remaining egg whites.
Scrape mixture into cake pan and smooth the top. Set cake pan in baking pan and place on oven rack. Pour enough boiling water into the baking pan to come about a third to halfway up the sides of the cake pan. Bake at 350 degrees F for exactly 30 minutes. The surface of the torte will spring back when very gently pressed but it will still be quite gooey inside.
Remove the cake pan and water pan from the oven. Remove the cake pan from the water and cool completely on a wire rack. Wrap the pan in plastic wrap and refrigerate overnight before serving. The dessert may be refrigerated for up to 2 days or frozen for up to 2 months.
Slide a thin knife or metal spatula around the sides of pan to release the torte. Place a piece of waxed paper on top of the torte. Invert a plate on top of the waxed paper and invert the torte onto the plate. Remove pan and peel away paper liner. Turn torte right side up again and remove waxed paper. Cut into wedges with a sharp thin knife. Dip the knife in hot water and wipe it dry between each slice. Or cut with dental floss like a moist cheesecake. Serve each slice with about 2 tablespoons of Raspberry Sauce (recipe on www.familycircle.com) and a dollop of Enlightened Whipped Cream (recipe on www.familycircle.com), if desired.