In an electric mixer, combine 1/4 cup water, yeast, and honey. Let stand until yeast is creamy, about 10 minutes. Add sponge and mix on low speed until combined, about 1 minute. Add remaining water, all the flours, rye meal, cracked wheat, and salt; mix, using the paddle, on low speed for 2 minutes. Change to dough hook and mix on medium-low speed until the dough is smooth and tacky, 8 minutes. Or knead by hand, 15 to 20 minutes.
Transfer dough to a floured surface and place smooth side up in a lightly oiled bowl, cover with plastic wrap, and let rise in a warm place until 1 1/2 times the size, 2 hours.
Punch dough down and fold it back onto itself 4 or 5 times. Turn folded side down, cover, and let rise in a warm place until doubled in bulk, 1 hour.
If using, sprinkle 2 braided Brotformen liberally with flour. Turn dough onto a lightly floured surface and cut in half. Cover one piece of dough loosely with oiled plastic wrap. On an unfloured surface, knead the other piece of dough into a ball. Cup your hands around it and move it on the work surface in small, circular motions, until top is rounded and bottom is smooth.
Place the shaped loaf, bottom up, in a Brotform. Cover loosely with lightly oiled plastic wrap and then with a towel. Repeat shaping process with second piece of dough. (If not using Brotformen, shape dough in the same way and place on parchment dusted with coarse cornmeal; coat the bottom and 1 inch up the sides with cornmeal. Cover loosely with oiled plastic wrap and then with a clean towel.) Let loaves rise in a warm place until doubled in bulk, about 1 hour. Thirty minutes before this final rise is completed, place a baking stone, if using, in lower third of oven and an empty baking pan on the lowest shelf. Heat oven to 450 degrees.
Transfer one loaf from a Brotform to a baker's peel or baking sheet sprinkled with coarse cornmeal. Using a razor or serrated knife, slash the top 1/4 to 1/2 inch deep. Slide the loaf onto the baking stone. Repeat with second loaf. If not using a baking stone, slash tops and bake on a cornmeal-dusted baking sheet. Quickly and carefully pour 2 cups of very hot water into the heated baking pan to create steam, and close the oven door. Bake until dark golden brown and hollow sounding when tapped on the bottom, about 25 to 30 minutes. If the bread darkens too quickly, lower temperature to 425 degrees after 15 minutes of the baking time. Let cool on a wire rack for at least 30 minutes before slicing.