Stir warm water, 1/2 cup bread flour, yeast, and sugar together in a bowl. Let stand until the yeast softens and forms a creamy mixture, about 40 minutes.
Mix 1/2 cup cornmeal, olive oil, and salt into yeast mixture. Gradually add bread flour to yeast mixture until a dough pulls together.
Knead dough on a lightly floured work surface until smooth and elastic, 10 to 12 minutes. Place dough in a large, lightly-oiled bowl and turn to coat. Cover with a damp towel and let rise in a warm place until doubled in volume, about 2 hours.
Turn dough out onto a lightly floured surface and roll into a 14-inch wide rectangle. Roll dough, starting from the long-end, into a loaf, finishing seam-side down.
Dust a baking sheet with 1 tablespoon cornmeal. Place loaf on baking sheet, cover with a dry towel, and let rise until doubled, about 1 hour.
Preheat oven to 425 degrees F (220 degrees C). Place a shallow pan of water on the lower rack of the oven.
Cut a 1/2-inch deep slash down the center of the loaf.
Bake in preheated oven until the top is golden brown and the bottom of loaf sounds hollow when tapped, 35 to 40 minutes. Cool on a wire rack.