This recipe is a version of Carol Field's from 'The Italian Baker'
She uses a yeast-based biga, but the version below uses a combination of sourdough starter and a small amount of yeast. You can also make it completely sourdough (see below), but I have found that it doesn't work quite as well.
Mix the starter, flour and water together. Leave in a warm place for 24 hours.
Warm the milk or soy milk until tepid, add the yeast, stir and leave for 10 minutes
Add the water and olive oil to the yeast/milk in a large bowl. Add in the starter. Break it up with your fingers.
Stir in the flour and salt, and mix to a ragged mess. Leave for 10 minutes.
Three quick (10 second) kneads at 10 minute intervals on an oiled surface. (This is a very moist dough, so you will need plenty of oil on your hands and surface. See tutorial on kneading  for details of this technique)
Cover the dough and leave for 1 1/2 hours
Divide the dough into four.
Prepare 4 pieces of baking paper - spread flour generously over the top.
On a well-floured surface roll one piece up tightly into a cylinder. Then with the seam facing up take hold of a pinch of the side of the dough and stretch it outwards. Work your way down each of the sides of the cylinder until it is in a rectangular shape about the width of your hand and the length of your forearm. Place the dough onto one of the floured pieces of paper seam side up. Dimple the dough vigorously with your fingertips. It will look not very promising. Repeat with the other pieces of dough. Cover them and leave for 1 1/2 to 2 hours.
Preheat the oven to 200C (or hotter) with a baking stone in place. Toss some semolina generously over a peel (eg piece of stiff cardboard).
Upturn one of the pieces of dough onto the peel (seam side now down). Peel off the baking paper gently. Spray with water. Slide the dough off the peel onto the baking stone.
repeat with the other pieces of dough
Bake for 20-30 minutes until the base is cooked.
NB to make 100% sourdough omit the yeast, and stretch out the proving times (to 3-4 hours before shaping, and then another 3-4 hours before baking)
I know that the recipe makes too much starter. However this can be a definite advantage. Take the remaining starter, and add 1 egg, a little (soy) milk and melted margarine. Blend until smooth in a food processor, or whisk by hand. Makes fantastic crepe batter...!