First activate the yeast: mix the starter ingredients together in a bowl (crumble the fresh yeast, if using), then cover with clingfilm. Set aside on the counter for an hour, until the dough has increased in size and bubbles are visible on its surface. Your starter is ready.
Begin the fougasse: sift the flour into a mixing bowl, add the tepid water, prepared starter, salt and olive oil. Mix well, then cover and set aside for 5 minutes. Transfer the dough to a clean, dry, lightly floured surface and begin to knead. Knead for 15 minutes until a stretchy, springy dough has formed, then shape into a ball and place back in the mixing bowl. Cover the bowl with clingfilm and place in a warm, draught-free spot to rise.
Once the dough has doubled in size, usually after 2–3 hours depending on the ambient temperature, knock back and knead once more briefly. Sprinkle flour over a baking tray and sit the dough on it. Roll into an oval shape, 2cm thick, then slice diagonal slits through the dough in a wheat pattern. Enlarge the holes using your fingers. Cover the fougasse with clingfilm or a damp tea towel and leave to rise again in a warm place for 1–2 hours. Towards the end of this prove, preheat the oven to 240˚C/220˚C fan/gas mark 9.
Remove the clingfilm or tea towel and lightly press olives into the surface of the dough. Pick the rosemary leaves off the sprigs and again lightly press into the dough. Sprinkle over the salt flakes, oregano and a little drizzle of olive oil.
Bake the fougasse for 15–20 minutes. It will not go darker than a pale golden brown, but check it is cooked by tapping the base and listening for a hollow sound. Fougasse is best eaten within 2 days.