Combine all-purpose and rye flour; stir well. Combine 2 cups flour mixture, cereal, cornmeal, yeast, and salt; mix well. Set remaining flour mixture aside.
Combine water, molasses, chocolate, and butter in a medium saucepan; heat mixture to 125°, stirring occasionally.
Gradually add hot liquid mixture to cereal mixture, beating at low speed of electric mixer 2 minutes. Add potatoes and 1 cup flour mixture; beat at high speed of electric mixer 2 minutes. Add caraway seeds and enough remaining flour mixture to form a soft dough, beating well after each addition.
Turn dough out onto a floured surface; cover and let rest 15 minutes. Knead 10 minutes or until smooth and elastic. Shape into a ball; place in a well-greased bowl, turning to grease top. Cover and let rise in a warm place (85°), free from drafts, 1 hour or until doubled in bulk.
Punch dough down; cover and repeat rising procedure 30 minutes. Punch dough down, and divide into 3 equal portions. Shape each portion into a ball. Place each ball in a greased 8- inch round cake pan. Cover and repeat rising procedure 45 minutes or until doubled in bulk.
Bake at 350° for 1 hour or until loaves sound hollow when tapped. Remove bread from pans immediately; cool on wire racks.