Beat margarine at medium speed of an electric mixer until creamy; gradually add 3/4 cup sugar and Lemon-Vanilla Sugar, beating well.
Combine flour and next 3 ingredients, and stir well. Combine milk and lemon juice. Add flour mixture to margarine mixturealternately with milk mixture, beginning and ending with flour mixture. Mix after each addition.
Beat egg whites and cream of tartar at high speed of an electric mixer until stiff peaks form. Fold beaten egg white into batter.
Spoon batter into an 8-inch angel food cake pan or a 9- x 5- x3-inch loaf pan coated with cooking spray. Bake at 350° for 45 to 50 minutes or until a wooden pick inserted in center comes out clean. Cool in pan on a wire rack 10 minutes. Remove from pan, and let cool completely on wire rack. Sift powdered sugar over cooled cake.
To make cupcakes, fill paper-lined muffin pans three-fourths full.