Two nights before you're planning to bake your bread, revive your starter: remove starter from fridge and let come to room temperature. Stir the starter well to recombine any liquid that may have gathered on the top. Measure out 1 cup of starter.

Place 1 cup starter in a large jar, bowl, or container, add 1 cup (250g) of water and 1.5 cups (225g) of flour and mix until combined. The mixture will be lumpy, like pancake batter. Cover loosely with plastic wrap and keep at room temperature overnight.

Refresh it once more in the morning with ¼ cup (65g) water and ⅓ cup (50g) flour, and once again that night with the same quantities (¼ cup (65g) water and ⅓ cup (50g) flour). The starter will be ready to use at night, or the next morning, when it bubbles and smells yeasty.

You will need 1 cup of refreshed starter.

When ready to bake, chop rosemary finely. Dump the bread flour and whole-grain flour into a mixing bowl, and stir with a wooden spoon to combine well. Add salt and chopped rosemary, and stir to combine.

Pour in the water and starter and stir together until just moistened. Beat 40 strokes, scraping the bottom and the sides of the bowl, until the dough forms a thick, spongy mass.

Transfer dough to an oiled crockpot or an oiled large glass bowl. Cover the bowl with plastic wrap or a large plate and let ferment at room temperature for 12 to 24 hours, or until the dough is bubbly on the surface, has a sponge-like appearance and has either doubled or risen by half.

Use right away or place the bowl, covered with plastic wrap, in the refrigerator for up to three days.

When dough is ready, place it on a generously floured surface and dust with more flour. Flour your hands. Using a dough scraper or floured hands, scrape the dough up and over itself, flouring and turning it as you go, for 12 to 15 turns, or until dough is soft and not sticky. Dust very lightly with flour.

With floured hands, work the dough as little as possible and form it into a wide 10-12 inch batard. Pinch the ends and all seams closed, and lightly flour sticky spots. The dough should be smooth and soft, and not sticky. If sticky, add a bit more flour.

Prepare a baking sheet or cutting board. Line it with a clean kitchen cloth, or parchment paper, and dust it with flour. Without moving your batard too much, use a dough scraper or well-floured hands to slide your dough onto the floured surface.

Cover the dough with plastic wrap sprayed with oil, oily side down. Let rest at room temperature for 5 to 8 hours.

About 30 minutes before baking, place a broiler pan on the bottom rack of the oven. Preheat oven to 450F.

Remove plastic wrap from batard. Using a sharp knife, make three to five crosshatch slashes diagonally across the top of the loaf.

Very carefully and wearing oven mitts, remove the hot baking sheet from the oven, and cover with parchment paper. Sprinkle the cornmeal on the paper. Using the dough scraper and well-floured hands, slide the bread from the pan onto the baking sheet, taking care to keep its shape.

Pull lower rack of the oven halfway out, and pour 2 cups of hot water into the broiler pan. Spray batard with water, but take care not to drench it. Return rack into the oven, and close oven door immediately.

Bake for 27 to 30 minutes, lightly spraying the loaf with water three times during baking. The bread will be ready when crust is golden-brown. Remove baking sheet from the oven, and, wearing kitchen gloves, remove bread onto wire rack to cool.