1. **Prepare the Levain (Optional)**: Ensure your sourdough starter is active and bubbly. Feed it 6-8 hours before you plan to mix your dough, aiming for it to be at its peak activity when ready to use.

2. **Autolyse**: In a large mixing bowl, combine the 350g water, 450g bread flour, and 50g whole wheat flour. Mix with your hands or a Danish dough whisk until no dry flour remains and a shaggy dough forms. Cover the bowl with a damp cloth or plastic wrap and let it rest for 30 minutes to 1 hour (autolyse). This allows the flour to fully hydrate.

3. **Mix the Dough**: After autolyse, add 100g active sourdough starter and 10g fine sea salt to the dough. Incorporate thoroughly by squeezing and folding the dough for 5-10 minutes until the salt is dissolved and the starter is evenly distributed. The dough will become stickier before it starts to come together. Cover.

4. **Bulk Fermentation**: Begin the bulk fermentation process at room temperature (ideally 72-78°F / 22-25°C). Over the next 4-5 hours, perform a series of "stretch and folds" to build strength in the dough. * **First Set (30 minutes after mixing)**: 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. * **Second Set (30 minutes after first set)**: Repeat the stretch and fold process. * **Third Set (1 hour after second set)**: Repeat the stretch and fold process. * **Fourth Set (1 hour after third set - Adding Inclusions)**: Gently flatten the dough slightly. Sprinkle the lemon zest and blueberries over the surface. Perform one more set of stretch and folds, being careful not to crush the blueberries too much, working them evenly into the dough. * **Rest**: Let the dough rest undisturbed for the remaining 1.5-2 hours, or until it has increased significantly in volume (about 30-50%) and feels airy. The timing will depend on your room temperature and starter activity.

5. **Pre-shape**: Lightly flour your work surface. Gently tip the dough out onto the surface. Using a bench scraper and floured hands, gently shape the dough into a loose round or rectangle. Cover with a damp cloth or inverted bowl and let rest for 20 minutes (bench rest).

6. **Final Shape**: Lightly flour your work surface again. Gently un-cover the dough. Shape the dough into a tight boule or batard, depending on your banneton shape. Aim to create tension on the surface of the dough without tearing it.

7. **Cold Proof**: Lightly flour your banneton or proofing basket. Carefully transfer the shaped dough, seam-side up, into the banneton. Cover with a plastic bag or plastic wrap and refrigerate for 12-16 hours (cold proof). This slows fermentation, develops flavor, and makes the dough easier to score.

8. **Preheat Oven & Dutch Oven**: About 45-60 minutes before you're ready to bake, place your Dutch oven with the lid in the oven and preheat to 450°F (232°C).

9. **Score and Bake**: Carefully remove the hot Dutch oven from the oven. Gently invert the cold dough from the banneton onto a piece of parchment paper, or directly into the hot Dutch oven. Score the top of the dough with a lame or very sharp knife (a single deep slash or a decorative pattern).

10. **Bake Covered**: Place the lid back on the Dutch oven and carefully return it to the hot oven. Bake for 30 minutes with the lid on.

11. **Bake Uncovered**: Remove the lid and continue baking for another 15-20 minutes, or until the crust is a deep golden brown and the internal temperature reaches 200-210°F (93-99°C).

12. **Cool**: Carefully remove the bread from the Dutch oven and transfer it to a wire rack. Let it cool completely for at least 1-2 hours before slicing. Slicing too early can result in a gummy texture.