Place the starter, water and honey into a stand mixer bowl

Whisk using the dough hook until frothy

Add the flour and salt and knead on a slow setting for 10 minutes

Cover the bowl and leave in a warm place to prove until doubled in size

Pour the oil into a large plastic container, coat the sides well with the oil

Lightly brush some of the oil onto cling wrap and a Swiss roll pan

Pour the dough into the plastic container and flip the dough over so that it is completely coated in oil

Cover with the cling film and leave to prove for 2 hours until nicely puffed up

Preheat the oven to 220° Celsius

Tip the dough into the baking tin and stretch to fit as best you can

Dimple the top with your fingertips, pushing right to the bottom of the tin

Place the onions, tomatoes and mozzarella onto the top and sprinkle with flaked salt

Bake for 30 minutes and leave to cool slightly before serving