"In a large glass bowl, combine the flour, yeast, salt, rosemary, and lemon zest. Add 1 ½ cups warm water (no hotter than 110°F) and stir until blended. The dough will be shapeless and shaggy and quite sticky. Cover and allow to rest overnight (up to 24 hours) at room temperature. The surface of the dough will become dotted with bubbles. When ready to bake, heat the oven to 450°F and bring a Dutch oven with lid to temperature inside the oven. (It is important that the knob on the lid of your Dutch oven or bread pot is able to withstand the 450°F temperature.)After 15 minutes, remove the Dutch oven and carefully insert the shaped dough into the pot. With a sharp knife or razor, cut slits into the top of your dough and add flakey sea salt, if desired. Return the lid to the pot and bake covered for 20 minutes. After 20 minutes, very carefully remove the lid and bake uncovered an additional 10-15 minutes -- just until the loaf is golden brown and gives a satisfying hollow sound when thumped. Allow to cool briefly before slicing. "