Combine flour, yeast, salt, and sugar in a bowl. Add lukewarm water and mix until a sticky dough forms. Coat with a teaspoon of olive oil, cover, and refrigerate for 18-24 hours.
Grease a 10" x 12" pan with parchment paper if needed. Oil hands, remove dough from bowl, and fold it over itself 4 times, turning the bowl each time. Repeat once more.
Add 2 tablespoons of olive oil to the pan, place dough, and coat with oil. Cover and let rise in a draft-free place for 2-4 hours, until doubled in size.
Preheat oven to 220°C. Sprinkle rosemary and remaining olive oil over dough. Dimple dough and sprinkle with sea salt.
Bake for 25-30 minutes until golden brown. Let rest 5 minutes before transferring to a cooling rack. Slice warm or cool completely.
Notes
For a lighter texture, proof the dough for 24 hours. For a denser bread, reduce proofing time to 18 hours.