In the bowl of a stand mixer, mix together the starter and water, then stir in flour and salt. Mix on low until a shaggy ball forms, then mix with olive oil for 5 minutes until smooth and elastic. Shape the dough into a ball and place in an oiled bowl.
Let rise for two hours, completing stretch-and-folds four times, every half and hour. (To stretch and fold: lightly wet your hands and gather your dough at the top of the bowl and lift with two hands towards the ceiling, lifting and stretching enough so that you can fold the dough over on itself, tucking it into the opposite side. Repeat on all four sides.)
After two hours, grease a 6 inch round pan with olive oil and line with parchment. Using lightly oiled hands, round the dough into a ball and transfer to the pan, cover with plastic and let rest for two hours at room temperature - there won’t be much of a rise, more of a spreading out and loosening of the dough. Place in the fridge overnight.
The next day, 1-3 hours before you want to bake, proof at room temp for 1-3 hours until the dough rises and becomes quite airy looking.
Heat the oven 445°F. Drizzle on olive oil and dimple the dough with your fingers, pushing your fingers all the way down to the bottom of the pan. Sprinkle with flaky salt and fresh rosemary. Bake for 15 minutes, rotate and continue to bake for 10 more minutes. Remove and let cool slightly, then remove from the pan and enjoy!