Combine the flour and salt in a large mixing bowl. Make a dent in the center and add in the starter. Mix with your hands to create a dough. Add a bit of warm water if it's too dry. Your dough should be soft and slightly sticky.
Sprinkle your workspace with some flour. Knead the dough on the floured workspace until it's smooth, silky, and elastic. If the dough is too sticky, sprinkle with a bit of flour. Knead for about 12-15 minutes.
Once the dough is smooth, silky, and elastic, lightly grease a large mixing bowl with olive oil. Put the dough in the bowl and cover with plastic wrap.
Place the dough in a cool, not cold place for up to six hours, until it's doubled in size.
Once it's doubled in size, place the dough on your floured work surface. Knock the air out of it and lightly knead for a few minutes. Roll the dough into a ball and place in a large mixing bowl. Cover with a tea towel and place in cool place to proof for 12 hours.
Once ready to bake, preheat oven to 475°. Place a roasting tin filled with ice cubes on the lowest shelf of the oven. The steam creates a lovely crust on your loaf.
Line a baking sheet with greaseproof paper and grease very lightly with a little olive oil. Gently lay the risen loaf onto the sheet (do not worry if you lose a little air from the loaf as you do this, it will come back in the oven). Place in the middle of the preheated oven and cook for 30 minutes, then lower the temperature to 400 F and cook for a further 20 minutes or until the loaf is golden brown, the outside crust crisp, and the bread sounds hollow when tapped on the base.
Place the loaf on a cooling rack, and leave to cool completely before eating. The sourdough will keep for up to a week.