Feed and check your starter (4–8 hours before or overnight). Use a bubbly, active starter. It should double (or show lots of bubbles) within a few hours after feeding.
Autolyse (30–60 minutes). In a large bowl, mix the 300 g water with the 500 g total flour (450 g bread flour + 50 g whole wheat if using) until there are no dry patches. Cover and rest 30–60 minutes.
Why: autolyse hydrates flour and helps gluten development.
Add starter + salt (5 minutes). Add 100 g starter and 10 g salt. Mix until incorporated — squeeze and fold the dough until homogeneous. Cover.
Bulk fermentation with stretch-and-folds (2–4 hours at ~75°F / adjust for temp).
Do 4 sets of stretch-and-folds every 20–30 minutes during the first 1.5–2 hours. To stretch-and-fold: wet hands, lift one side and fold over; rotate bowl and repeat 4×.
After the last fold, let dough rest undisturbed until it has increased by ~20–40% and shows bubbles at the surface. (Warmer temps shorten time; cooler temps lengthen it.)
Option A — Same day schedule: Bulk ferment ~3–4 hours total, then shape and final proof 1–2 hours (or until ~80% rise), bake.
Option B — Overnight retard (recommended for flavor): After initial bulk and folds (1.5–2 hours), shape lightly and place in a floured banneton, cover, and refrigerate overnight (8–16 hours). Bake next day from cold.
Shape: Turn dough onto a lightly floured surface, pre-shape into a round, rest 15–20 minutes, then final shape into a tight boule. Place seam-side up in a floured banneton (or bowl lined with linen).
Final proof: Room temp 1–2 hours until puffy (Option A) or fridge 8–16 hours (Option B).
Preheat oven + bake: Preheat oven to 475°F (245°C) with a Dutch oven inside for at least 45 minutes. Score the loaf, transfer dough seam-side down into hot Dutch oven, cover, bake 20 minutes covered, then reduce to 450°F (230°C) and bake 20–25 minutes uncovered until deep brown and hollow-sounding. Internal temp ~205–210°F when done.
Cool: Let cool at least 1 hour before slicing to finish crumb set.