In a small saucepan melt unsweetened chocolate and the margarine or butter over low heat, stirring occasionally. Remove from heat; cool. Grease and lightly flour an 8x8x2-inch baking pan; set aside. In a medium mixing bowl stir together flour, walnuts or pecans, and baking powder; set aside. In a large mixing bowl stir together the cooled melted chocolate mixture and the sugar. Add the eggs and vanilla. Using a wooden spoon, lightly beat mixture just till combined. (Do not overbeat or brownies will rise during baking, then fall and crack.) Stir in the flour mixture. Pour the batter into the prepared pan; spread to edges. Bake in a 350 degree oven for 40 minutes. Meanwhile, for topping, in a small saucepan melt the semisweet or bittersweet chocolate over low heat, stirring occasionally; cool slightly. In a medium mixing bowl beat cream cheese with electric mixer on medium speed about 30 seconds or till softened. Add the melted semisweet or bittersweet chocolate, egg, sugar, milk, and vanilla. Beat until combined. Carefully spread topping evenly over hot brownies. Bake in the 350 degree oven about 10 minutes more or till topping is set. Cool in pan on a wire rack. Cover; chill at least 2 hours. To serve, cut brownies into triangles or bars. (To cut into triangles, first cut into rectangles, then cut in half diagonally.) If desired, in a small saucepan melt 2 squares chocolate and shortening; drizzle over brownies and onto plate. Garnish with raspberries, if desired. Cover and refrigerate to store. Makes dozen to 16 servings.