Measure 100g of starter into a large bowl and pour over 400ml lukewarm water. Stir with a spatula to combine. Mix in the flour to make a rough dough. Cover and leave to rest for at least 30 mins or up to 1 hr.

Making focaccia is a sticky business. Have a bowl of water near you to dip your hands in. Scatter a small handfui of salt over the dough, dip a hand into the water and use it to mix the salt into the dough with your fingers. The dough should bounce back up slowly. Cover and leave for half an hour. Wet your hands, grab the dough from one side and stretch it. Repeat from the other side until it becomes very elastic. Cover and leave for another half hour. Repeat twice more then leave the dough to raise for 2-3 hours. It should be soft and about 1.5 cm thicker than it was originally.

Drizzle a deep baking tray with 1/3 of a glass of olive oil and use your fingers to mix the oil into the dough, stretching and folding the dough on the tray for 5-10 minutes. When the dough has become an oily elastic mass, leave to raise at room temperature for 3-4 hours, or for up to a day in the fridge.

Heat the oven to 220C/200C fan or gas 7. Use your fingers to stretch the dough so it fits into the tray evenly, then dimple the surface with your fingertips. Drizzle with 2 tbsps olive oil and dimple a few more times to create little oil puddles on the surface. Scatter over the remaining salt, give the dough a final poke and bake for 25-30 mins until puffed up and deep golden. Remove the tray from the oven, drizzle with the remaining oil then leave to cool.