A sourdough starter is needed to give this bread its characteristic taste and texture (as is the stretching, folding and resting process, essential for forming the desired air pockets in the baked loaf). You can make it yourself or buy it at specialty baking stores or online (or ask a friend for some of theirs). The starter needs to be ripe (or active) to perform its magic, meaning it's been fed within the last 8 to 15 hours, is bubbly and has doubled in volume.