01 - Dissolve the yeast and sugar in lukewarm water in a small bowl. Let stand for 10 minutes until the mixture becomes frothy and bubbly.
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, cohesive dough forms.
03 - Turn the dough onto a lightly floured surface and knead for 8 to 10 minutes, working it until it becomes smooth, supple, and springs back when pressed.
04 - Transfer the dough to an oiled bowl, cover with a damp kitchen towel, and set aside in a warm spot for 1 hour or until the dough has doubled in volume.
05 - Preheat the oven to 425°F (220°C). Grease a 12x16 inch baking tray generously with olive oil.
06 - Gently punch down the risen dough and place it on the prepared tray. Stretch and press it to fill the tray, using your fingertips to create deep dimples across the entire surface.
07 - Brush the surface generously with olive oil. Scatter the chopped rosemary and flaky sea salt evenly over the dough. Press olives or halved cherry tomatoes into the dimples if desired.
08 - Allow the topped dough to rise for 20 to 30 minutes until visibly puffy. Bake on the center rack 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 let the focaccia cool slightly on the tray before slicing into squares. Serve warm as an appetizer, sandwich bread, or accompaniment to soups and salads.