Measure water into a large (4-quart) bowl. Add whole-wheat flour, cover, and let stand about an hour.

Add freshly-fed starter and yeast, stir until thoroughly mixed.

Add all-purpose and bread flours and mix into a dough. Cover and let stand about 1 hour.

Sprinkle salt and vitamin C, if using, onto dough and fold in.

Turn out dough onto a floured work surface and knead for 5 minutes. Let dough rest for 5 minutes.

Repeat the kneading and resting cycle 3 more times, then transfer to a large bowl, cover, and let rise until doubled, about 90 minutes.

Gently turn out dough onto a floured surface and cut strips of dough that weigh about 200 g (about 6 inches long and 2 inches wide). While folding up cut edges, stretch and shape dough into a baguette about 16 inches long. Place seam side down on baking sheet lined with a silicone baking mat or parchment. Fit 3 baguettes on each baking sheet.

Cover with a clean towel and let rise until doubled, about 45 minutes.

Preheat oven to 450°F.

Using a razor, make 4 to 5 long diagonal slashes down each baguette and bake for 22 to 25 minutes, rotating pans from top to bottom and front to back after 15 minutes, or until golden brown

Remove to a rack and let cool completely.