1. 1. Combine Wet Ingredients and Starter: In a large mixing bowl, gently whisk together the active sourdough starter (or discard) with the warm water until well combined. The mixture should look milky and slightly bubbly if your starter is active.

2. 2. Add Dry Ingredients: To the wet mixture, add the all-purpose flour, granulated sugar, and salt. Use a sturdy spoon or your hands to mix until a shaggy dough forms and no dry flour remains. It doesn’t need to be perfectly smooth at this stage.

3. 3. First Fermentation (Bulk Rise): Cover the bowl with a damp kitchen towel or plastic wrap. Let the dough rest at room temperature (ideally 70-75 F) for 4-8 hours. During this time, the dough should noticeably increase in volume and become bubbly. If your kitchen is cooler, it might take longer.

4. 4. Incorporate Inclusions: After the bulk rise, gently turn the dough out onto a lightly floured surface. Flatten it slightly into a rectangle. Sprinkle the blueberries, lemon zest, and lemon juice evenly over the dough. Gently fold the dough over itself a few times, kneading lightly for about 1-2 minutes, just enough to distribute the inclusions without crushing the blueberries too much.

5. 5. Shape the Loaf: Form the dough into a round or oval loaf. If you have a banneton basket, lightly flour it and place the dough seam-side up. If not, place the shaped dough on a piece of parchment paper.

6. 6. Second Fermentation (Proofing): Cover the shaped dough with a damp towel or plastic wrap. Let it proof at room temperature for 1-3 hours, or for a deeper flavor development, place it in the refrigerator overnight (8-12 hours). The dough should look slightly puffy and pass the “poke test” (if you gently poke it, it should slowly spring back).

7. 7. Preheat Oven and Bake: About 30 minutes before baking, preheat your oven to 450 F (230 C) with a Dutch oven or baking stone inside. Carefully remove the hot Dutch oven. Score the top of the dough with a sharp knife or razor blade (a simple cross or a few slashes works well).

8. 8. Bake the Bread: Carefully transfer the dough into the hot Dutch oven (or onto the baking stone). Cover the Dutch oven and bake for 30 minutes. Remove the lid and continue baking for another 15-20 minutes, or until the crust is deeply golden brown and the internal temperature reaches 200-210 F (93-99 C).

9. 9. Cool Completely: Transfer the baked bread to a wire rack and let it cool completely for at least 1-2 hours before slicing. This step is crucial for the crumb to set properly and for the flavors to fully develop.