Separate eggs. Beat egg whites with 1/2 cup sugaruntil stiff. Melt margarine & chocolate together and cool. Beat egg yolks with 1/2 cup sugar until light, add chocolate mixture & beat. Fold in egg whites. Pour 3/4 of mixture into an ungreased pringform pan. Cover & refridgerate remaining 1/4 mixture. Bake cake for 30 minutes & cool. (as cake cools top will cave in- don't worry about this) When cake is cool, m pour remaining mousse mixture on the top & smooth. Decorate as desired with whipped cream or Kosher for Passover non- dairy topping. This cake also freezes well.