Dust the work surface with a little all-purpose flour for kneading. Add flour only as needed to keep from sticking to the work surface.
Add the all-purpose flour, semolina flour, and salt into the bowl with the sponge and stir until the dough and sponge form a loose, shaggy ball. Scrape the dough out onto the floured surface.
Knead the dough for about 5–7 minutes, or until smooth and elastic. The dough should be soft.
Spray a large bowl with cooking oil and place dough into the bowl. Cover with plastic wrap in a warm, draft-free spot for about 2 hours.
Dust the work surface with about 3/4 cup of flour. Dust the peel or sheet pan (without sides) with about 1/2 cup of the flour.
Punch down the dough, then pour dough out onto the surface. Shape the dough into a large, round loaf by bouncing it around on the flour. The dough will be light and airy, unlike other bread dough which is usually tight. Spray a towel with non-stick spray and place over the loaf. Let the dough rise until it's about doubled in size (45 minutes).
Preheat oven to 400 degrees. Remove the towel and sprinkle the top of the dough liberally with flour. Using a pastry scraper or sharp knife, cut through the dough length-wise and roll the dough onto the sheet pan or peel. If your sheet pan or peel is large enough, place both of the loaves onto them, making sure they are spaced far enough apart. They should be placed with the cut side up on the pan. Sprinkle a little extra kosher salt on the top of the loaves.
Bake the bread in the oven for about 35–45 minutes. TUrn off the heat and let the bread "crust" for about 10 more minutes. If using an earthen oven, place bread in the earthen oven for about 10 minutes. The bread is ready once it makes a hollow sound when tapped on the bottom. Transfer to a cooling rack and allow to cool. (I have a hard time with this! I like warm bread with lots of herb butter).