1 envelope dry yeast
1 teaspoon granulated sugar
1/4 cup warm water (105 to 115 degrees F)
1/2 ounces unsweetened chocolate
1 tablespoon margarine
1 1/4 cups water
1/4 cup dark molasses
2 tablespoons apple cider vinegar
1 tablespoon salt
1/2 cup All-Bran cereal
2 to 2 3/4 cups unbleached flour
1 1/2 cups rye flour
Sprinkle yeast and sugar over 1/4 cup warm water. Stir to dissolve. Let stand until foamy, about 10 minutes.
Melt chocolate and margarine with 1 1/4 cups water in a large bowl set over gently simmering water. Stir until smooth. Remove from over water. Blend in molasses, vinegar and salt. Mix in cereal. Let cool.
Grease a large bowl. Blend yeast into cereal mixture. Gradually stir in 2 cups unbleached flour and rye flour. Turn dough out onto lightly floured surface and knead until smooth and elastic, about 10 minutes, kneading in up to 3/4 cup more unbleached flour if needed to form a workable dough. Add dough to prepared bowl, turning to coat entire surface. Cover and let rise in warm area until doubled in volume, about 2 hours.
Grease two loaf pans. Punch dough down. Turn out onto lightly floured surface and let rest 3 minutes. Knead 3 minutes. Divide dough in half. Roll each into an 8 x 7-inch rectangle. Starting with long side, roll dough up into a cylinder. Tuck ends under and pinch seam to seal. Place seam side down in prepared pans. Cover and let rise in a warm place until doubled, about 1 1/2 hours.
Preheat oven to 375 degrees F. Bake until loaves sound hollow when tapped on the bottom, about 45 minutes.
Remove bread from pans. Let cool completely on a rack before serving.