In a large mixer bowl, combine 2 cups unbleached flour, bran flakes, yeast, brown sugar, salt and 1 teaspoon of optional fennel seed. In a heavy saucepan, heat 2 1/2 cups water, molasses, chocolate and oil, stirring until very warm, about 120-130 degrees Fahrenheit. Add liquid mixture to flour mixture and blend at low speed until ingredients are moistened. Beat 3 minutes at medium speed or by hand. Beat in rye flour plus enough unbleached flour to make a stiff dough.

Knead on a lightly-floured surface, adding 1/2-1 cup additional unbleached flour, until dough is smooth and elastic, about 10 minutes. Place in a greased bowl; turn to coat surface. Cover and let rise in a warm place, free from drafts, until doubled, about 90 minutes. Punch down dough; let rest, covered, for 15 minutes. On a lightly-oiled surface knead lightly, divide dough in half and shape into two loaves.

Place in two well-greased 8 1/2 by 4 1/2 by 2 1/2 inch loaf pans. Cover and let rise in a warm place, free from drafts, until doubled, 60-90 minutes. Bake in a preheated 375 degree Fahrenheit oven for 35 minutes; remove and brush tops with mixture of egg white and 1 tablespoon water. Sprinkle tops with remaining 1 teaspoon of optional fennel seed. Return to oven and bake for another 15 minutes or until crust is dark brown and loaves sound hollow when lightly tapped. Remove from pans; cool on wire racks. Note: If undersides of loaves are not sufficiently browned, turn out of pans and return loaves to oven for another 5-7 minutes. Makes 2 loaves