Replenish the original starter by removing 1½ cups of the sponge mixture and putting back into your original starter mixture. Mix well and keep in the refrigerator.
To the remaining sponge, add oil, salt, and two cups of flour. Mix well. Add more flour, 1/2 cup at a time, until the dough comes away from the sides of the bowl. You want a soft, slightly sticky dough.
Knead the dough 5 minutes, or mix in your stand mixer with a dough hook.
Divide the dough in half. Form into a circle and place on a parchment-covered baking tray. Let rise two hours.
Preheat the oven to 425° F.
Make slashes on the top of the loaves, being careful not to cut too deep. Brush with water if you want a crusty loaf. Bake for 20 minutes, then reduce heat to 375° F. I usually give my loaves another brush of water. Bake for another 20-30 minutes. If using a thermometer, the internal temperature should be about 195° F.
Cool on wire rack.