In a large bowl, combine warm water, sugar, and yeast. Let it sit for 5–10 minutes until foamy.
Add flour, salt, and olive oil. Mix until a soft and sticky dough forms.
Knead the dough gently for 5–7 minutes.
Place the dough in a well-oiled bowl, cover, and let it rise for 1–2 hours until doubled in size.
Grease a baking tray generously with olive oil and transfer the dough into it.
Gently stretch the dough to fit the tray. Cover and let it rest for 30–45 minutes.
Preheat the oven to 220°C (425°F).
Press your fingertips into the dough to create deep dimples.
Drizzle with olive oil and sprinkle with rosemary and sea salt.
Bake for 20–25 minutes until golden brown and crisp on top.
Let the focaccia cool slightly before slicing and serving.