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.
03 - Mix until a sticky dough comes together. Turn out onto a lightly floured surface and knead for 8 to 10 minutes until the dough is smooth and elastic.
04 - Place the dough in an oiled bowl, cover with a damp kitchen towel, and let rise in a warm spot for 1 hour or until doubled in size.
05 - Preheat the oven to 425°F. Generously grease a 12x16 inch baking tray with olive oil.
06 - 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 surface.
07 - Brush the surface generously with olive oil. Scatter the chopped rosemary and flaky sea salt evenly over the dough. Arrange olives or halved cherry tomatoes on top if desired.
08 - Allow the dough to rise for 20 to 30 minutes until puffy and swollen. Bake for 20 to 25 minutes until the top is deep golden brown and the bottom sounds hollow when tapped.
09 - Let the focaccia cool slightly on the tray before slicing into squares. Serve warm as an appetizer, sandwich base, or alongside soups and salads.