Icing sugar; sifted Butter an 8 inch springform pan, line with parchment paper, then butter paper and dust lightly with flour. To prevent leaking, line outside of pan with double thickness of heavy duty aluminium foil. Melt chocolate and butter, stirring occasionally, in top of double boiler set over simmering water. Cool slightly. Meanwhile, using electric beater, in a large bowl, beat egg yolks with 3/4 cup sugar on high until very light and lemon coloured, about 5 minutes; scrape down sides occasionally. Beat in melted chocolate mixture until well blended. In separate bowl, beat egg whites until frothy. Gradually beat remaining sugar; continue to beat whites until stiff. Gently fold in remaining egg whites. Pour batter into prepared pan. Place springform pan in larger pan filled with hot water, coming halfway up sides of springform pan. Bake on lower half of preheated 375F oven for 15 minutes. Reduce heat to 275F and bake 30 minutes. Turn off heat, prop door open slightly and leave cake in oven for 40 minutes. Remove pan from water; let cake cool completely in pan. Refrigerate overnight until cake sets. Carefully remove from pan and invert onto serving platter. Bring to room temperature before serving. Dust with icing sugar. Slice and serve with creme anglaise or whipped cream. SERVES: 8-10