Stir the yeast, sugar and 1/4 cup warm water in a large bowl (or in the bowl of a stand mixer). Let sit until foamy, about 5 minutes.
Add 1 tablespoon olive oil, the flour, 1 1/2 tablespoons rosemary, the fine salt and 3/4 cup warm water; stir with a wooden spoon (or with the dough hook if using a mixer) until a dough forms.
Turn the dough out onto a lightly floured surface and knead, dusting lightly with flour if necessary, until smooth and elastic, about 10 minutes. (Or knead with the dough hook on medium-high speed, adding a little flour if the dough sticks to the bowl, about 8 minutes.)
Brush a large bowl with olive oil. Add the dough, cover with plastic wrap and let stand at room temperature until more than doubled, about 2 hours.
Brush 2 baking sheets with olive oil. Generously flour a work surface; turn the dough out onto the flour and divide into 4 pieces. Working with one piece at a time, sprinkle some flour on the dough, then fold the top and bottom portions into the middle. Fold in the sides to make a free-form square. Use a spatula to turn the dough over, then tuck the corners under to form a ball. Place seam-side down on a prepared baking sheet. Repeat with the remaining dough, putting 2 balls on each baking sheet. Let stand, uncovered, until more than doubled, about 2 hours.
Preheat the oven to 400 degrees F. Bake the loaves 10 minutes; brush with the remaining 1 tablespoon olive oil and sprinkle with the kosher salt and the remaining 1/2 tablespoon rosemary. Continue baking until golden brown, about 10 more minutes. Transfer to a rack to cool. Serve with olive oil seasoned with pepper.