Combine Dry Ingredients: In a large mixing bowl, whisk together the flour, instant yeast, sugar, and salt.
Add Water and Oil: Add the warm water and 1/4 cup of olive oil to the dry ingredients. Stir with a wooden spoon or a spatula until a wet, sticky dough forms. It's okay if it looks rough; no kneading is necessary.
First Rise: Cover the bowl with plastic wrap or a clean kitchen towel. Let the dough rise at room temperature until it doubles in size, about 1 to 2 hours.
Prepare Pan: Drizzle a bit of olive oil in a 9x13 inch baking pan. Transfer the dough to the pan, spreading it out to the edges. If it springs back, let it rest for a few minutes before spreading again.
Second Rise: Cover the dough in the pan and let it rise again for about 30 minutes. Meanwhile, preheat your oven to 425°F (220°C).
Add Toppings: After the second rise, use your fingers to create dimples in the dough. Drizzle with more olive oil and sprinkle with coarse sea salt. Add any additional toppings like rosemary or cherry tomatoes if desired.
Bake: Place the pan in the oven and bake for 20-25 minutes, or until the top is golden brown.
Cool and Serve: Remove the focaccia from the oven and let it cool in the pan for a few minutes. Then, transfer it to a wire rack to cool slightly before cutting.
Enjoy: Slice your focaccia and serve it warm or at room temperature.