1. In a large mixing bowl, whisk together the all-purpose flour, instant yeast, and 2 teaspoons of sea salt. Make sure these are well combined before adding any wet ingredients.

2. Pour the warm water and 1/4 cup of olive oil into the dry mixture. Use a wooden spoon or a sturdy spatula to mix until all the flour is incorporated and a shaggy, sticky dough forms. Do not overmix; just combine until there are no dry spots.

3. Gently fold in the chopped Kalamata olives and fresh rosemary until they are evenly distributed throughout the dough. The dough will still be very wet and sticky at this point.

4. Cover the bowl tightly with plastic wrap or a clean kitchen towel. Let the dough rise at room temperature for 2-4 hours, or until it has doubled in size and is bubbly. For an even deeper flavor, you can refrigerate the dough overnight (8-12 hours) for a slow rise.

5. Once the dough has risen, generously drizzle a 9×13-inch baking pan with olive oil. Gently transfer the dough into the prepared pan.

6. Using oiled fingertips, gently press and dimple the dough all over, creating those characteristic focaccia indentations. Drizzle a little more olive oil over the top, and sprinkle with extra sea salt. Let the dough rest in the pan for another 20-30 minutes while your oven preheats.

7. Preheat your oven to 400 F (200 C). Bake for 25-30 minutes, or until the focaccia is golden brown on top and cooked through. The crust should be crisp and the interior soft and airy.

8. Once baked, remove the focaccia from the oven and let it cool in the pan for a few minutes before transferring it to a wire rack to cool completely. Slice and serve warm or at room temperature.