Place all ingredients in an extra-large bowl (it needs to be big enough for the biga to triple in size). Whisk together until the yeast has dissolved and all the flour has been incorporated into the water.
Cover the bowl with cling wrap and place in the fridge. The biga can be used after three hours, but for a stronger sourdough fermentation flavour, leave it for 24 hours.
Place water, then the biga, followed by flour and salt in a mixing bowl and bring together using a dough hook on low speed for three minutes.
Check: is it too firm? Does it need some water? Is it too soft? Does it need more flour? Adjust and mix for a further seven minutes — the dough should be firm but slightly tacky.
Remove dough hook and cover the dough in the mixing bowl with cling wrap. Leave for two to three hours until the dough has doubled in size.
Remove the dough and cut into five even pieces (about 260g per dough ball for a 12 inch pizza). Flatten the dough, sprinkle with flour and roll out to the size of the tray. Leave on tray for 30 minutes to 1 hour until the dough has doubled in size.