In a large mixing bowl, combine the warm water and instant yeast. Let it sit for about 5 minutes until frothy.
Add the flour, salt, and ¼ cup of olive oil to the yeast mixture. Stir until a rough dough forms.
Transfer the dough to a lightly floured surface and knead for about 5-7 minutes until smooth and elastic.
Place the dough in a greased bowl, cover it with a damp cloth, and let it rise in a warm place for about 1 hour or until doubled in size.
Once risen, punch down the dough to release the air, then turn it out onto an oiled baking sheet or a large, rimmed baking pan.
Gently stretch and press the dough to fill the pan evenly. Make a series of dimples all over the surface of the dough using your fingertips.
Drizzle olive oil over the top, then sprinkle the chopped rosemary and coarse sea salt. If desired, press halved cherry tomatoes into some of the dimples for extra flavor.
Let the dough rest for another 30 minutes while you preheat the oven to 425°F (220°C).
Bake the focaccia for 20-25 minutes or until golden brown and crisp on the outside.
Remove from the oven and let it cool slightly before slicing.
Notes
Serve warm, sliced into squares, and drizzle with olive oil or balsamic reduction for added flavor. Garnish with a sprig of fresh rosemary on top.