Mix 375 g (1½ cups + 1 Tbsp) lukewarm filtered water with 120 g (½ cup) active starter until dissolved.

Mix in 250 g (2 cups) flour. Add 11 g (about 2 tsp) salt, mix. Add remaining 275 g (2¼ cups) flour and mix until combined into a sticky, shaggy dough.

Cover and rest 30-40 minutes.

Stretch and fold: pull the dough up at the side of the bowl and fold it toward the center, rotating the bowl to fold every side. Cover and rest 30 minutes.

Repeat the stretch and fold three more times, for a total of 4 rounds, resting 30 minutes between rounds.

Bulk ferment 2-3 hours at room temperature, until risen about 50% (not doubled).

Loosen the dough from the bowl and turn it out onto a floured surface.

Pre-shape by folding the top edges in twice, then roll into a tight loaf, tighten the surface into a taut skin, and pinch the ends closed.

Flour the banneton well. Flip the dough in so the smooth shaped side is on the bottom, pinch the seam closed on top, dust with flour, and cover with a breathable cloth.

Refrigerate overnight.

Preheat oven with a Dutch oven inside to 475°F for 30 minutes.

Turn the dough onto parchment, score at a 45° angle, transfer to the Dutch oven, then add 4 ice cubes under the parchment paper.

Bake covered 30 minutes, then uncovered 10 minutes.

Move to a baking sheet and bake open 5 minutes more for a lighter crust (longer for darker).

Cool on a rack at least 1 hour, ideally 3, before slicing.