01 - In a large mixing bowl, whisk together the bread flour, salt, sugar, and instant dry yeast until evenly distributed.
02 - Pour in the lukewarm water and olive oil. Stir with a wooden spoon or your hands until a sticky, shaggy dough comes together.
03 - Turn the dough onto a lightly floured surface and knead for 8 to 10 minutes, until the dough becomes smooth, elastic, and springs back when pressed.
04 - Place the dough in a lightly oiled bowl, cover with a damp kitchen towel or plastic wrap, and let it rest in a warm spot for 1 to 1 1/2 hours, or until doubled in volume.
05 - Generously coat a baking tray (approximately 12x16 inches) with olive oil. Gently transfer the risen dough onto the tray and press it out evenly using your fingertips, creating characteristic dimples across the surface.
06 - Drizzle the remaining olive oil over the dough, scatter the rosemary leaves evenly, and sprinkle with flaky sea salt. Cover and let rise for another 30 minutes.
07 - While the dough completes its second rise, preheat the oven to 425°F. Bake the focaccia for 20 to 25 minutes until the top is golden brown and the loaf sounds hollow when tapped on the bottom.
08 - Remove from the oven and allow the focaccia to cool slightly on the tray. Slice into squares or strips and serve warm.