How to Make It
In a very large bowl, combine the warm water and milk. Stir in the honey until dissolved. Sprinkle the yeast on top and let stand until foamy, about 5 minutes. Using a wooden spoon, stir in the whole wheat flour and 3 cups of the all-purpose flour. Stir in the salt and olive oil, then stir in 5 cups more of the all-purpose flour.
Using a dough scraper, scrape the dough out onto a generously floured work surface. Using the scraper, lift and fold the wet dough while incorporating the remaining 2 cups of all-purpose flour. Knead lightly for a few minutes until a smooth, slightly sticky dough forms. Transfer the dough to a very large oiled bowl. Cover with plastic wrap and let rise overnight at room temperature.
Butter three 9-by-5-inch metal loaf pans. Punch down the dough and sprinkle it all over with the sunflower seeds. Scrape the dough out onto a generously floured work surface and knead it lightly, working in the sunflower seeds. Cut the dough into 3 equal pieces. Press each piece into a rectangle about 8 by 10 inches. Starting at a long end, roll up the dough, tucking in the sides neatly. Transfer the dough to one of the prepared loaf pans, seams down. Repeat with the remaining dough. Cover loosely with plastic wrap and let rise in a warm, draft-free spot until the top of the dough is just below the rim of the pans, about 1 hour.
Preheat the oven to 400°. Position a rack in the lower third of the oven. Lightly spray the tops of the loaves with water and bake for 10 minutes. Turn the heat down to 375° and bake the loaves for 20 minutes. Rotate the pans and bake for 25 minutes longer, or until the loaves sound hollow when turned out of the pans and tapped on the bottom. (If necessary, bake the loaves for another 10 minutes.) Turn the loaves out of the pans and let them cool on a wire rack. Serve the bread warm or at room temperature.