Mix together ripe/active sourdough starter with all-purpose or bread flour and water. Cover loosely and let sit 3-4 hours at 78-80°F until doubled, bubbly & peaked.

To a large bowl, mix together ripe levain with water, granulated sugar and lemon zest. Whisk together. Then add salt and bread flour. Mix together until a wet and sticky dough forms.

Cover and let rest for 30 minutes.

Perform a series of 'stretch and folds' over the next 1 ½ hours while incorporating blueberries.

Cover and let rise for 2-2.5 more hours at 78ºF.

Pre-shape and bench rest for about 30 minutes.

Shape the dough and prepare for cold fermentation, refrigerating overnight or up to 14-20 hours.

Preheat the Dutch oven to 450°F for 20 minutes.

Score the dough and bake in the Dutch oven at 425°F for 25 minutes, then at 400°F until fully baked.

Let cool completely before slicing.