Whisk ½ teaspoon yeast into ½ cup warm water (110°F/45°C) in a bowl and stir in whole wheat flour to make poolish starter. Beat until thick batter forms. Cover bowl and let sit at room temperature for 2–8 hours or refrigerate for 12–15 hours. Bring poolish to room temperature before using.

Combine poolish with 2 ½ cups warm water and ½ teaspoon yeast in a bowl. Gradually mix in bread flour, one cup at a time, until dough is difficult to stir.

Turn dough onto a floured surface and knead for 10–12 minutes, adding small amounts of flour if sticky. Sprinkle salt over dough and knead again for another 5–7 minutes until smooth.

Place dough in a lightly oiled bowl, cover, and let rise at room temperature until doubled, approximately 2–3 hours.

Punch dough down, divide into two pieces, and shape each into a round. Cover and let rest for 30 minutes.

Form rounds into baguette shapes. Place on a floured cloth with folds separating loaves. Dust tops with flour, cover, and let rise at room temperature until doubled, about 2 hours.

Preheat oven to 375°F (190°C).

Sprinkle a baking sheet with cornmeal and transfer risen loaves seam-side down. Slash tops with diagonal cuts.