In a large mixing bowl, whisk together the bread flour, kosher salt, granulated sugar or honey, and instant yeast until well combined.
Create a well in the center of the dry ingredients and pour in the warm water and 2 1/2 tablespoons of extra-virgin olive oil. Use a wooden spoon to mix until a rough dough forms.
Transfer the dough onto a lightly floured surface and knead it for about 5-7 minutes until smooth and elastic. Add flour if too sticky.
Grease a large bowl with olive oil, place the dough inside, and cover with a kitchen towel. Allow it to rise in a warm place for 1-2 hours until doubled in size.
Grease a baking sheet with olive oil. Punch down the dough and transfer it to the baking sheet. Stretch and press the dough into the pan, making dimples across the surface.
Cover the dough with a kitchen towel and let it rise for another 30-45 minutes until airy and light.
Preheat the oven to 425°F (220°C) for a crispy crust.
Drizzle the dough surface with extra virgin olive oil and sprinkle flaky sea salt. Add chopped fresh rosemary or other toppings if desired.
Bake the focaccia for 20-25 minutes until golden brown and hollow sounding when tapped.
Remove from oven and cool in the pan for a few minutes, then transfer to a wire rack to cool completely. Slice and serve.