In a large bowl, mix sourdough starter, warm water, honey, and vanilla until smooth. Add bread flour, salt, and lemon zest, stirring until a rough dough forms.

Knead on a floured surface for 5–7 minutes until smooth and elastic, adding a little extra flour if sticky. Cover and rest for 30 minutes.

In a small bowl, blend cream cheese, sugar, and lemon juice until creamy. Gently fold blueberries into the rested dough, keeping them whole.

Over the next 2 hours, perform stretch-and-folds every 30 minutes to build structure.

After the final fold, spread the cream cheese mixture over the dough and fold lightly to create a marbled swirl.

Shape into a round or oval loaf, place seam-side up in a floured proofing basket, cover, and refrigerate overnight.

Preheat the oven and Dutch oven to 450°F (230°C). Transfer the dough seam-side down into the hot pot, cover, and bake for 20 minutes. Remove the lid and bake another 15–20 minutes until golden. Cool completely on a wire rack before slicing to preserve the swirl.