In medium saucepan, combine sugar and cornstarch. Stir in milk. Cook and stir over moderate heat until thickened and bubbly. Remove from heat; cool to lukewarm. Add vanilla and yogurt. Refrigerate until mixture is cold. Melt chocolate. While chocolate is hot, pour it very slowly into chilled yogurt mixture while stirring gently. Freeze in ice-cream maker according to manufacturer's directions; or follow refrigerator-freezer instructions previously posted. Food & Wine RT [*] Category 4, Topic 6 Message 7 Wed Nov 06, 1991 D.MORRISSEY [DEE] at 00:03 EST MM by QBTOMM and Sylvia Steiger, GEnie THE.STEIGERS, CI$ 71511,2253, GT Cookbook echo moderator at net/node 0.8