01 - In a large mixing bowl, whisk together the flour, salt, sugar, and instant 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 - Shape the dough into a ball and place it in a lightly oiled bowl. Cover with a damp kitchen towel or plastic wrap and let it rise in a warm spot for 1 to 1½ hours, or until doubled in volume.
05 - Generously oil a baking sheet (approximately 12x16 inches). Transfer the risen dough onto the tray and gently stretch it out to fill the pan. Press your fingertips firmly into the surface to create classic dimples across the entire dough.
06 - Drizzle the remaining olive oil over the dimpled dough. Scatter the rosemary leaves evenly across the surface and finish with a generous sprinkle of flaky sea salt.
07 - Cover the tray loosely and let the dough rise for another 30 minutes until puffy. Meanwhile, preheat your oven to 425°F (220°C).
08 - Place the tray in the center of the oven and bake for 20 to 25 minutes, until the top is deeply golden brown and the bottom sounds hollow when tapped.
09 - Remove from the oven and allow the focaccia to cool slightly on the tray. Slice into squares or strips and serve warm.