Combine 1-1/2 cups all-purpose flour, rye flour, cornmeal, undissolved yeast and salt in large mixer bowl. Heat milk, potato water, molasses, bran cereal, chocolate, mashed potato, and butter until very warm (120° to 130°F), making sure chocolate has melted. Gradually add to flour mixture. Beat 2 minutes at medium speed of electric mixer, scraping bowl occasionally. Stir in caraway seeds and enough remaining all-purpose flour to make a stiff dough. Knead on lightly floured surface until smooth and elastic, about 8 to 10 minutes. Cover; let rest 10 minutes.
Divide dough in half; shape into smooth balls. Place in 2 greased 8-inch round pans. Cover; let rise in warm, draft-free place until doubled in size, about 45 minutes.
Bake at 350°F for 30 to 35 minutes or until done. Remove from pans; cool on wire racks.