Step 1In the bowl of a stand mixer, or in a medium bowl, mix together the wheat and rye flours, flaxseeds, salt and water until all of the flour is hydrated and the ingredients form a ball of dough. If working with a stand mixer, transfer the ingredients to a medium bowl. Cover the bowl loosely with plastic wrap and leave at room temperature for 12 to 24 hours.
Step 1In the bowl of a stand mixer, or in a medium bowl, mix together the flour, yeast and water to form a ball of dough. Using wet hands, knead the dough in the bowl for 2 minutes to make sure all of the ingredients are evenly distributed and the flour is fully hydrated. The dough should feel very tacky. Set the dough aside to rest for 5 minutes, then knead it again for 1 minute. The dough will become smoother but will still be tacky. Transfer the dough to a clean bowl, cover tightly with plastic wrap and refrigerate for at least 8 hours.
Step 1About 2 hours before mixing the final dough, remove the biga from the refrigerator. It will have risen slightly but probably will not be doubled in size.
Step 2Using a metal pastry scraper, chop the soaker and the biga into 12 pieces each (sprinkle some extra flour over them to keep the pieces from sticking together).
Step 3If mixing by hand, combine the soaker and the biga pieces in a bowl with the wheat flour and the seeds, salt, yeast and honey. Stir vigorously with a mixing spoon or knead with wet hands until all of the ingredients are evenly integrated and distributed into the dough, about 2 minutes. The dough should be soft and slightly sticky.
Step 4If using a stand mixer, put the soaker and biga pieces into the bowl along with the flour and the seeds, salt, yeast and honey. Mix on low speed with the dough hook for 1 minute to bring the ingredients together into a ball. Then continue to mix on medium-low speed, occasionally scraping down the bowl, until the doughs become cohesive and combined, about 3 to 4 minutes. Add more flour or water as needed until the dough is soft and slightly sticky.
Step 5Dust a work surface with flour, then roll the dough in the flour to coat. Knead the dough by hand, incorporating only as much extra flour as needed, until the dough feels soft and tacky but not sticky, 3 to 4 minutes. Form the dough into a ball and set it aside to rest on the work surface for 5 minutes while you prepare a clean, lightly oiled bowl.
Step 6Resume kneading the dough for 1 minute to strengthen the gluten and make any final flour or water adjustments. Form the dough into a ball and place it in the prepared bowl, rolling to coat with oil. Cover loosely with plastic wrap and let rise at room temperature for about 45 to 60 minutes, until about 1 1/2 times its original size.
Step 7Transfer the dough to a lightly floured work surface and form it into either a loaf pan shape or a free-standing batard. For loaf pan bread, place the dough in a greased 4- by 8 1/2-inch bread pan. To form a batard, gently stretch the dough into a long rectangular or oval shape, then gather the sides of the dough together to form a tube and pinch the seam closed (a batard is similar to a baguette, but slightly larger). Place the dough, seam side down, on a sheet pan lined with parchment paper dusted with flour. Brush the top of the dough with water and generously sprinkle the sesame seeds on top. Cover loosely with plastic wrap and set aside to rise at room temperature until it's about 1 1/2 times to double in size, 45 minutes to an hour.
Step 8Bake the loaf: If baking in a loaf pan, heat the oven to 350 degrees. Bake the loaf on the middle rack until puffed and lightly browned with a soft crust and a thermometer inserted reads 190 degrees, 45 minutes to 1 hour.
Step 9If baking a free-standing loaf, set the oven to 425 degrees, place a baking stone on the bottom rack of the oven and place a steam pan on the bottom of the oven. When the dough is ready to bake, score it (for hearth bread) and place it in the oven. Pour about 1 cup of hot water into the steam pan, lower the temperature to 375 degrees and bake for 15 minutes. After 15 minutes, rotate the bread and continue baking the loaf until it is a rich brown on all sides, sounds hollow when thumped on the bottom, and registers at least 200 degrees in the center, an additional 20 to 30 minutes.
Step 10Transfer the bread to a cooling rack (if baked in a pan, remove it from the pan immediately), and allow it to cool for 1 hour before serving.