To make the poolish, whisk 1/2 teaspoon yeast into 1/2 cup warm water — 110 degrees F (45 degrees C) — in a bowl. Stir in whole wheat flour until resembles a thick batter. Beat for about 100 strokes to form longs strands of gluten. Cover bowl with a damp cloth and let sit at room temperature for 2 to 8 hours (longer is better for flavor development). You can also ripen in the refrigerator for 12 to 15 hours, bringing poolish back to room temperature before proceeding with the recipe. Poolish is ready when bubbly and loose, with a yeasty, sour aroma.

Scrape poolish into a bowl; stir in 2 1/2 cups warm water and remaining 1/2 teaspoon yeast until combined. Add bread flour, 1 cup at a time, mixing well after each addition, until dough becomes too difficult to stir.

Turn dough out onto a floured work surface and knead for 10 to 12 minutes, adding more flour only when dough becomes too sticky to handle. Sprinkle salt over dough; continue kneading until smooth and springs back to the touch, 5 to 7 minutes more. Shape dough into a round; cover with a damp cloth for 5 to 10 minutes.

Place dough in a large, lightly oiled bowl and turn to coat. Cover with a damp cloth and let rise at room temperature until doubled in volume, 2 to 3 hours.

Punch down dough to deflate; cut into two pieces. Shape into two rounds, cover with plastic wrap or a damp cloth, and allow to rest for 30 minutes at room temperature.

Form dough rounds into baguettes. Place a heavily floured cloth on a baking sheet, arranging a fold down the center to separate the loaves. Place loaves, seam-sides up, on the floured cloth. Dust loaf tops with flour, cover with a damp cloth, and let rise until doubled in volume, about 2 hours.

Preheat the oven to 375 degrees F (190 degrees C).

Sprinkle a separate baking sheet with cornmeal. Gently transfer risen loaves to prepared baking sheet, seam-sides down. Slash loaves several times on the diagonal with a serrated knife or razor blade.

Immediately place scored loaves in the preheated oven; bake until loaves are golden brown, about 25 to 30 minutes. Cool loaves on wire racks.