Dissolve yeast in warm water. Add to the flour and mix until a shaggy dough forms. Cover with a damp cloth and let rest at room temperature for 12-24 hours to develop flavor.
Add salt and remaining water to the biga. Knead firmly on a floured surface for 10-15 minutes until smooth and elastic. Form into a tight ball, cover, and let double in size (about 2 hours).
Drain the San Marzano tomatoes. Using your hands, crush them gently into a bowl. Season simply with a pinch of sea salt. Do not cook the sauce!
Preheat your oven or pizza stone to the highest setting (ideally 450°C/840°F). Stretch the dough ball using your hands into a 12-inch circle. Spoon the crushed tomatoes evenly, add torn mozzarella, basil leaves, and a swirl of olive oil.
Slide the pizza onto the hot stone. Bake for 60-90 seconds in a pizza oven, or 8-10 minutes in a conventional oven until the crust is blistered and the cheese is bubbling.