Recipe by: Los Angeles Times Melt butter with chocolate and cocoa in microwave oven or stove top in double boiler. Transfer to mixing bowl to cool slightly. Use mixer to whip egg yolks, sugar, water, salt and vanilla on high speed 2 minutes. Add chocolate mixture on low speed, then flour. Whip egg whites and cream of tartar in clean mixing bowl until they hold soft, moist peaks. Thoroughly mix in 1/4 of egg whites into cake batter. Gently fold in remaining whites. Transfer to greased (8-inch) springform pan, bottom lined with greased foil and floured. Wrap outside of spring form with foil to eliminate any leakage. Bake at 300 degrees until wood pick inserted in center comes out moist (but not with wet crumbs), about 40 minutes. Do not overbake. Cool 1 hour in pan. Carefully remove from pan. Can be held overnight at room temperature, well covered, or frozen as long as 2 months. Serve at room temperature with powdered sugar pressed through fine sieve to coat top. Makes about 8 servings. NOTES : This cake bakes into a thin, dense and moist layer. It slices neatly into small portions for guests who just want a taste. By Abby Mandel Copyright Los Angeles Times ----