Feed your sourdough starter 8-12 hours before starting.

Combine lukewarm water, fed sourdough starter, sugar, vanilla extract, bread flour, whole wheat flour, and salt in a mixing bowl until shaggy dough forms.

Cover the bowl and let the dough rest for 30 minutes (autolyse).

Perform stretch-and-folds every hour for a total of three sets.

Gently incorporate dried blueberries into the dough, folding them in carefully.

Transfer the dough back to a bowl, cover it, and let it rise until it increases by about 50%.

Shape the dough into a ball and place it seam-side up in a floured banneton. Cover and refrigerate for 12 to 48 hours.

Preheat the oven to 500°F and place a Dutch oven inside.

Remove the hot Dutch oven, place the dough inside, score the top, cover, and bake for 30 minutes, then remove the lid and bake for an additional 10-15 minutes.

Let the bread cool completely on a wire rack before slicing.