In a large mixing bowl, combine 1 cup of active sourdough starter with 1 cup of lukewarm water and 1 teaspoon of salt. Gradually incorporate about 3 cups of bread flour, stirring until no dry flour remains. Cover the bowl with a damp cloth and let it rest for 30 minutes.

After the resting period, perform a stretch-and-fold technique every 30 minutes for 2 to 3 hours. Gently lift one side of the dough and fold it over the center until all sides have been folded.

During the second round of stretching, gently fold in the zest of 1 lemon and 1 cup of fresh blueberries, taking care not to burst the blueberries.

Cover the bowl with plastic wrap and let the dough ferment until it doubles in size, about 4 to 6 hours.

Lightly flour a clean surface, turn the dough out, and preshape it into a round loaf. Let it rest for 20 minutes.

Transfer the shaped loaf to a well-floured banneton, seam side up, and let it rest for 1 to 2 hours or cold-proof in the refrigerator overnight.

Preheat your oven to 450°F (230°C) with a Dutch oven inside, about 30 minutes before baking.

Carefully remove the Dutch oven, flip the loaf onto parchment paper, score the top with a sharp blade, and place it into the Dutch oven.

Bake covered for 30 minutes, then remove the lid and bake for an additional 15 to 20 minutes until golden brown.

Allow the bread to cool for at least one hour before slicing.