Put the flour and 1 teaspoon of sea salt into a large bowl and make a well in the middle. In a jug, mix the yeast into 300ml of lukewarm water, then gradually pour it into the well, stirring and bringing in the flour from the outside to form a dough.
Knead on a flour-dusted surface for 10 minutes, or until smooth and springy. Place back in a lightly oiled bowl, cover with a damp tea towel and leave to prove in a warm place for 1 hour, or until doubled in size.
Meanwhile, destone the olives and peel the garlic (if using), and then pound with the sun-dried tomatoes into a rough paste in a pestle and mortar. Add most of the basil leaves and a small pinch of salt, and bash again until you have a paste. Finely grate in most of the Parmesan, add a big pinch of black pepper, then muddle in 4 tablespoons of olive oil.
On a lightly floured surface, divide the bread into 2 equal pieces, then roll and stretch out into 2 identical circles roughly about 28cm wide. (If you want to be super-neat you can cut around a dinner plate for a perfect circle shape.) Place one of the circles on a lined baking sheet, then spread the olive paste all over the dough right to the edge, then tear over the mozzarella. Cover with the other circle and press down lightly to seal.
Position a jam jar, or something similar, in the centre, and then carefully make 12 evenly spaced cuts, starting from near the glass all the way out to the edge.
One by one, pick up each piece of bread and twist 3 times before laying neatly back down on the tray, poke in the remaining basil leaves in and around where you can, then cover lightly with a damp cloth and leave to prove again in a warm place for 1 hour or until doubled in size.
Preheat the oven to 190°C/375°F/gas 5. When the bread is ready, finely grate over the remaining cheese and drizzle over a little olive oil, then gently place in the middle of the oven for 20 to 25 minutes, or until golden.
Leave to rest for 15 minutes before tucking in.
Use a shop-bought pesto if you don’t want to make your own; experiment with different cheeses and herbs to mix it up.