Ballon is French for “balloon,” which is what these puffy round rolls resemble when they are done.

1. To make the sponge, combine 1 cup water and half the yeast, stir to dissolve, and let stand 5 minutes. Add 1 cup flour and beat 1 minute. Cover and let stand at room temperature 8–12 hours.

2. Add to the sponge 2 cups water, remaining yeast, butter, sugar, salt, and enough bread flour to make a soft dough. Turn out onto a floured work surface and knead 8–10 minutes. Add flour only to reduce stickiness.

3. Return to bowl, dust with flour, cover with plastic wrap, and rise at room temperature until doubled in volume, about 1 hour. Punch dough down, fold it in half, and rise again until doubled, about 45 minutes.

4. Line two baking sheets with parchment and sprinkle with cornmeal. Turn risen dough onto a floured surface. Shape into a rope, about 2″ thick. Slice 2″ pieces off the rope, then roll each into a tight ball.

5. Place balls onto prepared pans, 2″ apart. Dust with flour, cover loosely with plastic wrap, and proof for 30 minutes. Preheat oven to 375°F.

6. Place a pan of cold water at the bottom of the oven to create steam. Bake until golden brown and hollow sounding, about 15–20 minutes. Cool completely on a rack.