In a medium bowl, whisk together the flour, kosher salt, sugar and dry yeast.
Add the warm water. Using a spatula or wooden spoon, mix together until it forms a sticky dough ball. Don't overmix.
Rub the surface of the dough with some olive oil to keep it moist. Cover the bowl with a damp kitchen towel or plastic wrap (tightly-- I use a rubber band) and place in a warm place for about 2 hours. I set my oven on warm for about 5 minutes, turn it OFF and place the covered bowl inside. It creates a nice warm place for the dough to rise.
Grease a 8 or 9" cake pan with oil or nonstick cooking spray.
After the 2 hours, use a wooden spoon or spatula to deflate the dough and release it from the sides of the bowl, pulling it slightly towards the center. Pour a tablespoon of olive oil into the center of the baking pan. Turn the dough into the greased and oiled pan, and roll the dough ball in the oil to coat it all over. It will be a very soft and fluid dough ball.
Let the dough ball rest and rise for 3-4 hours in your already warm oven. No need to cover it if it's oiled properly.
After 3-4 hours, take pan out-- the dough will have risen and spread out to fill the pan. Preheat oven to 425 degrees F. Sprinkle the rosemary all over the dough. Pour another tablespoon of olive oil over the dough. Dip your fingers in the oil, then using all of your fingers, press straight down all over the top to create deep dimples. This is the fun part! Sprinkle with flaky sea salt all over. Be generous with the salt.
Transfer the pan to the oven and bake for 25-30 minutes until it looks golden and crisp. Your kitchen will smell amazing! Remove from oven and slice a knife around the edges to loosen (you may need to slip a spatula under to make sure it doesn't stick). Transfer to a cooling rack and cool for 10 minutes. Slice and enjoy!