Place the sourdough starter (300ml of tepid water and 600g strong white bread flour, half the olive and salt) into a large bowl or a mixer with a dough hook and knead for five minutes. The dough should be fairly sticky. Lightly grease a bowl with the remaining olive oil, add the dough, cover with cling film and leave to prove at room temperature for five hours or in the fridge overnight.
Once the dough has proved, return to the bowl or mixer, add the remaining flour and water and knead for 10 minutes, return to the bowl, cover with cling film and allow to prove for another two hours in a warm place.
Preheat the oven to 230°C/ 400°F/ gas mark 8.
Line a baking sheet if making a loaf or, if making baguettes, prepare the baguette tins.
Remove the dough from the bowl, knock back for two minutes and shape into a loaf, dust with semolina, cover with a damp cloth and allow to prove for a further hour.
Place a small ramekin of water into the bottom of the oven: this will help the loaf to rise.
Once risen, slash the top with a sharp knife and bake in the oven for approximately 30 minutes.