In a medium mixing bowl stir together flour, baking powder, soda, and salt. Cut in margarine or butter until mixture resembles coarse crumbs. Stir in raisins, if desired. Make a well in the center of the mixture.
In a small mixing bowl combine egg white and buttermilk. Add all at once to dry mixture. Stir just until moistened.
On a lightly floured surface knead dough 10 to 12 strokes until nearly smooth. Shape into a 7-inch round loaf.
Lightly coat a baking sheet with cooking spray Place bread dough on baking sheet. With a sharp knife, make 2 slashes in the top to form an X.
Bake in a 375 degree F oven about 30 minutes or until golden. Serve warm. Makes 1 loaf (16 servings).