In a large bowl, combine the warm water, granulated sugar, and active dry yeast. Give it a gentle stir and let it sit for 5-10 minutes, or until the mixture becomes foamy. This tells you your yeast is alive and ready to work!

Add the all-purpose flour, kosher salt, and 1/4 cup of extra virgin olive oil to the yeast mixture. Mix with a sturdy wooden spoon or spatula until a shaggy, cohesive dough forms. It doesn't need to be perfectly smooth at this stage.

Lightly oil a clean large bowl with a drizzle of olive oil. Transfer the dough to this bowl, turning it once to coat all sides. Cover the bowl tightly with plastic wrap or a damp kitchen towel. Let it rise in a warm place for 1 to 1.5 hours, or until it has visibly doubled in size.

Drizzle about 2 tablespoons of olive oil into a 9x13 inch baking pan, ensuring the bottom is well coated. Gently transfer the risen dough into the prepared pan, turning it once to coat in the oil. Using your hands, gently stretch the dough to mostly fill the pan. It's okay if it springs back a bit. Cover the pan again with plastic wrap or a damp towel and let it rest for another 15-20 minutes.

Preheat your oven to 400°F (200°C). Uncover the dough in the pan. Using oiled fingertips, gently press dimples all over the surface of the dough, trying to go almost all the way to the bottom. Scatter the halved Kalamata olives and chopped fresh rosemary evenly over the dough, pressing them lightly into the dimples. Drizzle generously with an additional 1-2 tablespoons of olive oil and sprinkle with flaky sea salt.

Bake for 20-25 minutes, or until the focaccia is golden brown on top and cooked through. The bottom should also have a nice golden hue.

Carefully remove the focaccia from the pan and transfer it to a wire rack to cool for at least 15 minutes before slicing and serving. This allows it to set properly and ensures a perfect texture.