Feed your starter 4–8 hours before baking so it’s active and bubbly. A floating test (a spoonful in water should float) tells you it’s ready.
Mix the dough. In a large bowl, stir together the starter and warm water until mostly dissolved. Add the flour and salt, mixing until a shaggy dough forms. It will look rough and sticky, that’s perfect.
Autolyse. Cover the bowl with a towel and let it rest for 30 minutes. This allows the flour to hydrate and makes stretching easier.
Stretch and fold. Over the next 2 hours, perform 4 rounds of stretch and folds every 30 minutes: grab one side of the dough, stretch it up, and fold it over itself. Turn the bowl and repeat on all four sides.
Bulk rise. Cover the bowl and let it rise at room temperature for 6–8 hours, or until doubled and bubbly.
Shape the dough. Gently turn the dough out onto a floured surface. Shape into a round by folding the edges toward the center, then flip seam-side down. Place it on parchment paper in a bowl or banneton, seam side up.
Second rise. Cover and refrigerate overnight (8–12 hours). This cold ferment deepens flavor and improves structure.
Preheat oven. Place a Dutch oven (with lid) inside and heat to 450°F.
Score and bake. Remove dough from the fridge, turn it seam-side down on parchment, and score the top with a sharp knife. Carefully place into the hot Dutch oven. Cover and bake for 25 minutes, then uncover and bake for 20 more minutes, until deep golden brown.
Cool completely. Place the loaf on a wire rack for at least 1 hour before slicing. The steam inside needs to settle for the crumb to set.