01 - In a large mixing bowl, combine bread flour, whole wheat flour, sourdough starter, and water. Mix thoroughly until no dry flour remains visible. Cover the bowl with a damp towel and let autolyse for 45 minutes to develop gluten structure.
02 - Add sea salt to the dough and knead briefly by hand for 2-3 minutes until fully integrated. Cover and let the dough rest for 30 minutes to allow the salt to hydrate evenly.
03 - Perform 3-4 sets of stretch-and-fold techniques at 30-minute intervals during the first 2 hours of bulk fermentation. Grab one edge of the dough, stretch it upward, and fold it toward the center. Rotate the bowl and repeat for all four sides.
04 - While the dough ferments, beat softened cream cheese, granulated sugar, and vanilla extract in a small bowl until completely smooth and creamy. Set aside at room temperature for easy spreading.
05 - During the final stretch-and-fold set, gently incorporate blueberries and lemon zest into the dough. Use a light folding motion to distribute evenly without crushing the berries.
06 - Turn the dough onto a lightly floured work surface. Using your hands, pat the dough into a rectangular shape approximately 1/2 inch thick. Spread the cream cheese mixture evenly across the surface, leaving a 1-inch border. Roll the dough tightly from the long edge into a jelly-roll style log, pinching the seam firmly to seal.
07 - Shape the rolled dough into a tight round or oval loaf. Place the dough seam-side up in a floured proofing basket or bowl lined with a well-floured towel. Cover and refrigerate for 6-10 hours (overnight) for cold fermentation.
08 - Place a Dutch oven or lidded cast iron pot in the oven and preheat to 450°F for at least 30 minutes to ensure thorough heating of the cooking vessel.
09 - Turn the proofed dough onto a piece of parchment paper. Use a sharp knife or lame to score the top of the loaf with a 1/2-inch deep cut. Sprinkle with coarse sugar and additional lemon zest if desired.
10 - Carefully transfer the loaf with parchment paper into the preheated Dutch oven. Cover with the lid and bake for 25 minutes to create steam and develop oven spring.
11 - Remove the Dutch oven lid and continue baking for 20 additional minutes until the crust is deep golden brown and sounds hollow when tapped on the bottom.
12 - Transfer the bread to a wire cooling rack and let cool completely for at least 2 hours before slicing. This allows the crumb structure to set and prevents the cream cheese from becoming too runny.