In a large bowl, mix together water and wheat flour. Cover and let stand several hours.

Add starter and mix until combined. Cover and let stand until bubbling, about 2 to 3 hours.

Add bread flour, salt, and vitamin C, if using. Use a bowl scraper to fold in and mix dough. Cover.

For the next 2 hours, every 15 to 30 minutes, fold the dough over itself about 15 times. Replace cover.

Refrigerate dough overnight, up to 15 hours. It will be about doubled in size.

Deflate dough and shape into a ball. Cover and let rise until doubled again, 3 to 5 hours.

Prepare proofing baskets by lining with towels and sprinkling with flour.

Carefully turn out dough unto floured surface, divide into 3 pieces and shape each into a ball, trying to minimize deflation. Set, rough side up, in proofing baskets. Proof until dough is very soft.

Preheat oven and dutch oven or combo-cooker to 450°F.

Place ball of dough on lid of dutch oven. Slash. Cover with dutch oven and bake 20 minutes. Remove cover and bake an additional 20 minutes. Remove to cool. Repeat with remaining loaves.