Heat semisweet chocolate in heavy 2-quart saucepan over low heat, stirring constantly, until melted; remove from heat. Stir in margarine. Stir in whipping cream and cashews.Refrigerate 10 to 15 minutes, stirring frequently, just until thick enough to hold a shape. Drop mixture by teaspoonfuls onto aluminum foil-covered cookie sheet. Shape into balls. (If mixture is too sticky, refrigerate until firm enough to shape.) Freeze 30 minutes.Heat shortening and chocolate chips over very low heat, stirring constantly, until chocolate is melted and mixture is smooth; remove from heat. Dip truffles, one at a time, into chocolate. Place on aluminum foil-covered cookie sheet. Immediately sprinkle some of the truffles with finely chopped nuts if desired.Refrigerate truffles about 10 minutes or until coating is set. Drizzle some of the truffles with a mixture of 1/4 cup powdered sugar and 1/2 teaspoon milk if desired. Refrigerate just until set. Serve at room temperature. Store truffles in airtight container. 15 Candies; 165 Calories Per Candy.