Add lukewarm water and sugar to the bowl of a stand mixer and mix briefly.

Sprinkle the yeast over the water and sugar mixture and set aside for about 5 minutes until the yeast activates and becomes foamy.

In a separate bowl, whisk together the bread flour and salt.

Fit the stand mixer with the dough hook, start on low speed and add the flour mixture. Mix a few minutes until a shaggy ball forms.

Increase the mixer to medium-low and knead the dough for about 10 minutes, until it becomes sticky and smooth.

Grease a bowl with olive oil and, using a greased spatula, transfer the dough to the bowl. Cover with plastic wrap or a towel and let rise until doubled, about 1 to 1 1/2 hours (or use the oven's "Proof" setting).

Brush a 9×13-inch baking dish with about 2 tablespoons of olive oil. Uncover the dough, oil your hands, and fold the dough into itself around the bowl to form a rough ball. Transfer the dough to the prepared pan and turn to coat in oil. Press the dough to the pan edges, cover, and let rise until doubled, about 45 minutes. Start preheating the oven to 425°F about 30 minutes into this rise.

Remove the cover, drizzle the remaining olive oil over the dough, then use oiled fingers to make indentations across the surface, pressing down to the pan. Sprinkle with flaky sea salt and rosemary if using.

Bake in the preheated 425°F oven for 20 to 30 minutes, or until golden brown. Remove from oven and cool slightly before slicing and serving.