Preparation

• Use a wooden spoon or sturdy spatula to stir together the water, half the oil, the yeast, kosher salt, sugar and flour in a large (five- or six-quart) bowl, forming a rough dough. Transfer to a container with a lid; partially cover and let it rest for about two hours on the counter. (Alternately, if you have a lidded container large enough for mixing, you can assemble the dough in there.) The dough can then be used right away, but it is much easier to handle once it has been thoroughly chilled. The dough can be stored in the refrigerator for up to two weeks.
  Place a baking stone on the middle oven rack; preheat the oven to 425 degrees. Pour the remaining oil into a 9-inch cake pan and evenly coat the bottom of the pan.
  Dust the surface of the refrigerated dough lightly with flour, then pull half of it off (it will be about a 1-pound portion; the dusting makes this task easier, as the dough is sticky). Dust the half you are using with more flour and quickly shape it into a ball by stretching the surface of the dough around to the bottom on all four sides, rotating the ball a quarter-turn as you go.
  Use your hands to flatten it into a half-inch-thick round six to seven inches in diameter. Place the dough top-side-down in the cake pan, moving it around a bit to coat it with the oil. It will not fill to the edges of the pan. Turn the dough over, cover the pan with plastic wrap, and let the dough rest for 10 to 15 minutes.
  Use your hands to gently push the dough to the edges of the cake pan. Sprinkle with the rosemary and coarse or flaky salt, as needed.
  Cover with plastic wrap, and allow the dough to rest and rise for 20 minutes.
  Place the cake pan on the heated baking stone in the oven. Bake for 20 to 25 minutes, or until the focaccia crust is medium brown and feels dry and firm on the surface. The baking time will vary, depending on the focaccia’s thickness.
  Use a rounded knife to loosen the loaf from the edges of the pan, then transfer the focaccia to a cutting board. Cut into wedges and serve warm, or allow to cool completely.