01 - Combine bread flour, whole wheat flour, sourdough starter, and water in a large bowl. Mix thoroughly until no dry flour remains visible. Cover the bowl and allow the dough to autolyse for 45 minutes.
02 - Add the fine sea salt to the dough and knead briefly until fully incorporated. Cover and let the dough rest for 30 minutes to allow gluten development.
03 - Perform 3 to 4 sets of stretch-and-fold technique at 30-minute intervals throughout the first 2 hours of bulk fermentation. This strengthens the gluten network for better texture.
04 - While the dough ferments, beat the softened cream cheese with granulated sugar and vanilla extract until smooth and fully combined. Set aside until ready to use.
05 - During the final stretch-and-fold cycle, gently incorporate the fresh 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 surface and press into a rectangle. Spread the cream cheese mixture evenly across the surface. Roll the dough tightly like a jelly roll and pinch the seams firmly to seal.
07 - Shape the filled dough into a tight round or oval. Place seam-side up in a floured proofing basket. Cover and refrigerate for 6 to 10 hours, preferably overnight, for slow cold fermentation.
08 - Preheat your oven to 450°F with the Dutch oven inside. Allow at least 30 minutes for thorough heating to ensure proper oven spring and crust development.
09 - Turn the dough onto parchment paper, score the top with a sharp knife or lame, and sprinkle with coarse sugar and extra lemon zest if desired. Bake covered for 25 minutes, then uncover and continue baking for 20 minutes until deep golden brown and crusty.
10 - Allow the loaf to cool completely on a wire rack before slicing to prevent the filling from becoming runny. Slice thick and serve toasted with additional cream cheese or lemon curd.