Combine yeast and warm water in a large bowl or pitcher. Using a wooden spoon add in 1 cup of the flour and salt and mix until combined. Stir in the rest of the flour one cup at a time, until completely incorporated. Cover with plastic wrap or a lid that is not shut completely. Allow to rise for 1 hour. Do not punch down the dough. Lightly oil the bottom of a cast iron skillet (a 10″ or 12″ skillet works well). Sprinkle a good amount of flour on top of the dough and then cover hands with flour. Take all of the dough and shape into a disk. (it will be sticky)! Place in the skillet, cover loosely with a towel, and allow to rise for another 30 minutes. Preheat the oven to 400ºF. Drizzle a little more oil over the top of the bread, and slash the dough with a knife creating an X. Sprinkle with coarse salt and rosemary leaves. Bake for 35-40 minutes until the top is a deep brown color.