Day 1: Firstly make the Soaker. Mix first 7 ingredients together (whole wheat flour, oat bran, flaxseeds,salt and water - excluding the additional tbsp whole wheat flour) in a bowl for about 1 minute until all of the flour is hydrated and the ingredients form a ball of dough.
Cover loosely with plastic wrap and leave at room temperature for 12 - 24 hours. (If it will be more than 24 hours, place the soaker in the refrigerator; it will be good for up to 3 days. Remove it 2 hours before mixing the final dough to take the chill off.).
Now make the Biga. Mix the next 3 ingredients together (whole wheat flour, yeast, water) in a bowl to form a ball of dough. Using wet hands, knead the dough in a bowl for 2 minutes to be sure the ingredients are evenly distributed and the flour is fully hydrated. The dough should feel tacky. Let the dough rest for 5 minutes, then knead again with wet hands for 1 minute. The dough will become smoother but still be tacky.
Transfer the dough to a clean bowl, cover tightly with plastic wrap and refigerate for at least 8 hours and up to 3 days.
About 2 hours before mixing the final dough, remove the Biga from the refigerator to take off the chill. It will have risen slightly but need not have risen significantly in order to use in the final dough.
Day 2: Chop the Soaker & Biga dough into 12 pieces each. Combine the Soaker & Biga pieces in a bowl with all the other ingredients except the extra flour and stir vigorously with a mixing spoon or knead with wet hands for about 2 minutes, until all of the ingredients are evenly integrated and distributed into the dough. The dough should be soft and slightly sticky; if not add more flour or water as needed. If using a mixer put the pre-dough pieces all all the other ingredients except the extra flour into the mixer with the dough hook attachment an mix on slow speed for 1 minute to bring the ingredients together into a ball. Then mix on medium-low speed for 2 - 3 minutes, until the pre-doughs become cohesive and assimilated into each other. Add more flour or water as needed until the dough is soft and slightly stickly.
Dust a work surface. Knead by hand for 3 - 4 minutes. Form dough into a ball and let it rest for 5 minutes while preparing a clean and lightly oiled bowl.
Resume kneading the dough for 1 minute to strenghten the gluten and make any final flour or water adjustments. Form the dough into a ball and place in the prepared bowl, rolling to coat with flour. Cover loosely with plastic wrap and let rise at room temperature for 45 - 60 minutes until it is 1 1/2 times its original size.
Transfer the dough to a lightly floured work surface and form it into a loaf pan. Lightly brush or spray with oil. Leave to rise again for 45 - 60 minutes until 1 1/2 times original size.
Pre-heat oven to 220 degrees Celsius When dough is ready to bake, place it in the oven along with a steam pan holding 1 cup of boiling water. Lower temperature to 180 degrees C and bake for 20 minutes. Rotate the loaf 180 degrees and continue baking for another 20 - 30 minutes until the loaf is a rich brown colour on all sides, sounds hollow when thumped on the bottom.
Transfer to a cooling rack and allow to cool for at least 1 hour before serving.