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 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 surface and knead for 8 to 10 minutes, until the dough is smooth, elastic, and springs back when pressed.
04 - Place the dough in an oiled bowl, cover with a damp kitchen towel, and let it rise in a warm spot for 1 hour or until doubled in bulk.
05 - Preheat the oven to 425°F (220°C). Generously grease a 12x16 inch baking tray with olive oil.
06 - Gently punch down the risen dough and transfer it to the prepared tray. Stretch and press the dough to fill the tray, using your fingertips to create deep dimples across the entire surface.
07 - Brush the dough generously with olive oil. Scatter the chopped rosemary and flaky sea salt evenly over the surface. Arrange olives or halved cherry tomatoes on top if desired.
08 - Let the topped dough rest and rise for 20 to 30 minutes until it looks puffy and has filled in the dimples slightly.
09 - Bake on the center rack for 20 to 25 minutes until the top is deep golden brown and the bottom sounds hollow when tapped.
10 - Allow the focaccia to cool in the pan for 5 to 10 minutes before slicing into squares. Serve warm on its own or paired with your favorite dip.