In a small jar or bowl, combine the active sourdough starter, 30g freshly milled whole wheat flour, and 30g water. Mix until well combined, cover loosely, and let ferment at room temperature (70-75°F / 21-24°C) for 8-12 hours, or until it has doubled in size, is very bubbly, and passes the float test.

Freshly mill the 400g whole wheat flour. In a large mixing bowl, combine the freshly milled flour with 300g of water. Mix by hand until no dry bits of flour remain. Cover the bowl with plastic wrap or a damp kitchen towel and let it rest for 30-60 minutes. This step, called autolyse, helps the flour absorb water and begin gluten development.

Add the ripe levain, salt, and olive oil to the autolysed dough. Begin mixing by hand or with a stand mixer on low speed. Once the ingredients are roughly incorporated, gradually add the remaining 20g of water (if needed) while continuing to mix. Knead the dough for 8-15 minutes (longer by hand) until it becomes smooth, elastic, and passes the windowpane test.

Transfer the dough to a lightly oiled clean bowl. Cover with plastic wrap or a damp towel. Over the next 4-6 hours (depending on ambient temperature), perform 3-4 sets of 'stretch and folds'. For each set, gently stretch a portion of the dough up and fold it over itself. Rotate the bowl and repeat 3-4 times until all sides have been stretched and folded. Do this every 30-45 minutes. The dough should increase in volume by 50-75% and show signs of activity like bubbles.

Gently turn the dough out onto a lightly floured surface. Using a dough scraper, gently shape the dough into a loose rectangle or round. Cover lightly and let rest for 15-20 minutes. This allows the gluten to relax.

Lightly grease a 9x5 inch loaf pan. Gently flatten the dough into a rectangle. Fold the top third of the dough down towards the center, then fold the bottom third up and over the top. Press out any air. Roll the dough tightly from one end to the other to create a log. Pinch the seam closed. Place the shaped dough, seam-side down, into the prepared loaf pan.

Cover the loaf pan loosely with plastic wrap or a damp towel. You have two options for final proofing: - **Cold Proof (Recommended for flavor development):** Refrigerate for 8-16 hours. This slows down fermentation and enhances flavor. - **Warm Proof:** Let rise at room temperature (70-75°F / 21-24°C) for 2-3 hours, or until the dough has visibly expanded and passes the 'poke test' (a gentle poke leaves a slight indentation that slowly springs back).

About 30-45 minutes before baking, preheat your oven to 425°F (220°C) with a rack in the middle. If desired, score the top of the loaf with a sharp knife or razor blade. Place the loaf pan in the preheated oven. Bake for 20 minutes. Then, reduce the oven temperature to 375°F (190°C) and continue baking for another 20-25 minutes, or until the crust is deeply golden brown and the internal temperature reaches 200-210°F (93-99°C).

Once baked, immediately remove the loaf from the pan and transfer it to a wire cooling rack. Allow the bread to cool completely for at least 2 hours before slicing. Slicing too early can result in a gummy texture.