To make the sponge:

Cup of Yum
1. In a small bowl, sprinkle the yeast over the lukewarm water and stir to combine. Allow to rest for 10 minutes, then stir in the 1 tablespoon flour.
2. Cover and rest at room temperature for 30 minutes.

To make the Broa:

1. Place the cornmeal in the bowl of a stand mixer fitted with a dough hook or a large bowl.
2. Stir the salt into the boiling water and pour the water over the cornmeal. Mix well until all of the cornmeal is wet.
3. Set aside for 15 minutes.
4. Mix in the flour, butter, and sponge. Slowly add additional lukewarm water as needed to form a dough.
5. Knead the dough on a lightly floured surface, then place back in the bowl, cover, and allow to rise at room temperature until doubled, about 2 hours.
6. Shape the risen dough into a round loaf, taking care not to deflate it. Add a sprinkling of flour to the top, cover with a towel, and allow to rise at room temperature for 30 minutes.
7. Preheat oven to 500˚F (260˚C) with baking stone on the center rack.
8. Place a deep pan filled with water on the bottom rack.
9. Transfer the puffed loaf to the hot baking stone and bake for 10 minutes.
10. Reduce temperature to 400˚F (200˚C) and continue to cook until the loaf is golden, another 15-20 minutes.
11. This bread is best the day it is baked.