In a large mixing bowl or the bowl of a stand mixer, combine warm water, sugar (or honey) and instant yeast. Stir gently and let sit 5–7 minutes until foamy. If it does not foam, your yeast may be inactive; start over with fresh yeast. Add 3 1/2 cups of the flour, the salt, and 3 tablespoons (0.1875 cup) of the olive oil to the yeast mixture.

Knead

If using a stand mixer fitted with a dough hook, mix on low/medium-low for 4–6 minutes until dough is smooth, elastic, and slightly tacky. If kneading by hand, turn dough onto a lightly floured surface and knead 6–8 minutes, gradually adding up to the remaining 1/2 cup flour as needed to keep dough workable but still slightly sticky. The dough should be soft and pillowy, not stiff.

First rise

Lightly oil a large clean bowl with ~1 teaspoon olive oil and place the dough inside, turning once to coat. Cover bowl tightly with plastic wrap or a damp kitchen towel and let rise in a warm draft-free spot until roughly doubled, about 1 to 1.5 hours (depending on room temperature).

Shaping & Second Rise

Prepare pan

Generously oil a 9x13-inch (or similar size) baking pan with about 1 tablespoon olive oil, making sure the oil coats sides and bottom to prevent sticking and to help create a golden crust.

Shape dough

Gently deflate the risen dough and transfer it to the oiled pan. Using your oiled hands, stretch and press the dough to fit the pan evenly, creating dimples with your fingertips as you go. If the dough resists, let it rest 10 minutes, then continue.

Second rise

Cover the pan lightly with plastic wrap or a damp towel and let the dough rise again until noticeably puffy, about 30–45 minutes.

Topping & Bake

Dimple & top

Preheat the oven to 450°F (230°C) while the dough finishes its second rise. With oiled fingers, press dimples into the dough across the entire surface. Drizzle 2 tablespoons olive oil evenly over the dough so it pools in some dimples. Sprinkle chopped rosemary and scatter the optional cherry tomatoes and sliced red onion if using. Finish with coarse or flaky salt sprinkled evenly.

Bake

Place the pan in the preheated oven and bake for 18–22 minutes until the top is deep golden brown and the edges are crisp. Rotate the pan once halfway through baking for even color if your oven has hot spots.

Finish & cool

Remove the focaccia from the oven and immediately drizzle an additional 1–2 teaspoons of olive oil over the top if desired. Let the focaccia rest in the pan for 5–10 minutes, then transfer to a wire rack. Slice and serve warm or at room temperature.