01 - Dissolve the yeast and sugar in lukewarm water in a small bowl. Let the mixture stand for 10 minutes until it becomes frothy and bubbly on the surface.
02 - Combine the bread flour and salt in a large mixing bowl. Create a well in the center and pour in the activated yeast mixture along with the olive oil. Stir until a sticky, shaggy dough comes together.
03 - Turn the dough out onto a lightly floured work surface and knead for 8 to 10 minutes, until the dough is smooth, supple, and springs back when gently pressed.
04 - Transfer the dough to a bowl coated with olive oil, cover with a damp kitchen towel, and let it rise in a warm spot for 1 hour, or until doubled in volume.
05 - Preheat the oven to 425°F. Grease a 12×16-inch baking tray with olive oil. Gently deflate the risen dough and place it on the tray, stretching and pressing it to fill the pan while creating deep dimples with your fingertips.
06 - Generously brush the surface with olive oil. Scatter the chopped rosemary and flaky sea salt evenly over the dough. Arrange olives or halved cherry tomatoes across the top if desired.
07 - Let the shaped dough rise for 20 to 30 minutes until visibly puffy. Bake on the center rack for 20 to 25 minutes, until the top is deep golden brown and the bottom sounds hollow when tapped.
08 - Allow the focaccia to cool on the tray for 5 to 10 minutes before slicing into squares or rectangles. Serve warm alongside soups and salads, or enjoy on its own.