In a large bowl, whisk together the flour and the salt.
In a small bowl or liquid measuring cup, add 225 grams (about 1 cup) warm water. Sprinkle on the instant yeast.
Stir the yeast into the water then add to the bowl with the flour and salt. Use a silicone spatula to mix well, until everything comes together in a shaggy ball. Scrape down the sides if needed, then cover and let rest for 30 minutes.
After 30 minutes, use lightly wet hands (or you can use nitrile kitchen gloves) and complete a set of stretch and folds, picking up the dough and folding it over on itself. Cover and rest for 30 minutes.
After resting, complete a set of coil folds, sliding your slightly wet (or gloved) hands underneath the bulk of the dough and picking it up over the bowl, letting the weight of the dough fall down. Tuck the ends under each other, turn the bowl 90 degrees and do another coil fold.
At this point, you can cold ferment your dough in the fridge (see the above post) or transfer the dough to an olive oiled cake pan.
Gently press the dough out to the edges and dimple slightly with oiled hands. Cover and proof for 30 minutes.
After 30 minutes, lightly oil your hands and dimple the dough again. Cover and let rest for another 30 minutes or until completely doubled and very poofy.
Heat the oven to 450°F and drizzle the top of the focaccia generously with olive oil. Dimple one last time and sprinkle on flaky sea salt and fresh rosemary.
Bake for 20-25 minutes or until the top of the focaccia is golden and crisp and the focaccia is cooked through (you can use an instant read thermometer inserted into the middle, it should read between 190–210°F). Remove and let cool for 30 minutes, then slice and enjoy!