Dust a large flat baking tray with flour.
Mix flour, salt, yeast, olive oil, and up to 250ml warm water in a bowl to form a soft dough.
Knead the dough for 10 minutes by hand or 5 minutes with a mixer until stretchy and springy.
Shape the dough into a 30cm x 20cm oval on the baking tray and cover with oiled clingfilm.
Preheat the oven to 200°C.
Let the dough rise for one hour until doubled in size.
Press deep holes into the dough every 4cm and insert 3cm rosemary sprigs.
Sprinkle with sea salt and bake in the top third of the oven for 25 to 30 minutes.
Drizzle with extra olive oil and cool on the tray.