Feed starter 4–12 hours before baking until doubled and bubbly
Mix dough: combine 450 g bread flour, 50 g whole wheat (optional), 350 g water (hold back 20 g), 100 g active starter, and 10 g salt
Mix until no dry flour remains; rest 20–30 minutes (autolyse)
Knead or fold until dough is smooth and elastic; adjust with reserved water if needed
Bulk ferment at warm room temperature until dough rises about 30–50%
Perform stretch-and-folds during bulk: 3–5 sets, spaced 20–30 minutes apart
Optional: pre-shape after bulk reaches target rise
Shape into a tight boule or batard; place seam-side up in a floured or lined proofing basket
Proof in refrigerator 8–16 hours (or at room temperature 1–3 hours until puffy)
Preheat oven to 475–500°F (245–260°C) with Dutch oven and lid on for 30–60 minutes
Transfer dough to parchment; score with a sharp blade
Bake covered 20–30 minutes
Bake uncovered 15–25 minutes until deep golden brown
Cool on a rack at least 1–2 hours before slicing