In a large mixing bowl, combine the yeast and water. Add half the flour in and stir with a wooden spoon. Add the rosemary, salt and remaining flour and stir until combined. Cover with plastic wrap and let rise in a warm place until doubled in size, about 1 hour. Or, you can let the dough rise in the skillet (next step).

Brush 2 tablespoons olive oil over the bottom of a 10 or 12-inch cast iron skillet. Sprinkle the dough and your hands with flour before shaping it into a disk. Dough will be sticky, it doesn’t have to shape perfectly. Place in the skillet, cover loosely, let rise until puffy, about 30 minutes.

Meanwhile, preheat the oven to 400°F.

Drizzle additional olive oil over the top of the bread. Slash the dough with a sharp knife to create an X shape. Sprinkle with rosemary leaves. Bake for 20 minutes. Remove from oven and sprinkle all over with the Parmesan cheese. Return to oven and bake for an additional 20 minutes, or until golden brown.