Grease and lightly flour an 8x4x2- or 7-1/2x3-1/2x2-inch loaf pan. Set pan aside.
In a medium mixing bowl stir together flour, granulated sugar, and baking powder. Add the milk, egg or egg white, 2 tablespoons margarine or butter, and vanilla. Beat with an electric mixer on low to medium speed about 30 seconds or until combined. Beat on medium to high speed for 1 minute. Pour batter into prepared pan.
Bake in a 350 degree F oven 20 to 25 minutes for the 8-inch pan or 25 to 30 minutes for the 7-1/2-inch pan or until a wooden toothpick inserted near the center comes out clean. Cool on a wire rack for 5 minutes. Remove cake from pan. Cool thoroughly on a wire rack.
For chocolate glaze, in a small saucepan melt chocolate and 1 tablespoon margarine or butter over low heat, stirring frequently. Remove from heat. Stir in the powdered sugar and hot water. Stir in additional hot water, if needed, to make glaze of drizzling consistency.
Spoon glaze over cake, allowing excess to drip down the sides. Makes 4 servings.