Spray 5-cup mold with nonstick cooking spray; sprinkle with sugar. In medium saucepan, bring milk to a boil over medium heat. Stir in rice. Reduce heat; simmer about 5 minutes, stirring constantly. Cover; cook about 45 minutes or until milk is almost absorbed and rice is tender and creamy, stirring occasionally.
In small bowl, combine 1/2 cup sugar and gelatin; stir into rice mixture until dissolved. Stir in chocolate, margarine and 1 teaspoon vanilla. Cool 30 minutes or until completely cooled, stirring occasionally.
Reserve 2 to 3 tablespoons whipped cream for garnish. Fold remaining whipped cream into rice mixture. Pour into sprayed mold. Cover; refrigerate at least 2 hours. Place serving platter in refrigerator to chill.
Meanwhile, to prepare custard, in heavy saucepan or in top of double boiler, combine eggs, 1/4 cup sugar and salt. Gradually stir in half-and-half. Cook over low heat, stirring constantly, until mixture coats spoon, about 10 minutes. DO NOT BOIL. Remove from heat; stir in 1 teaspoon vanilla. Cover; refrigerate until cool.
Just before serving, dip mold into hot water. Invert and shake onto chilled serving platter. Garnish with reserved whipped cream and, if desired, chocolate curls. Serve with custard. Store any remaining dessert and custard in refrigerator.