I used the recipe from Peter Reinhart "The Bread Baker's Apprentice" - the Biga version.
My Biga was my white sourdough, mixed with an equal amount of organic bread flour and some water to make a firm starter.
I used half the oil given in Reinhart's recipe. I proved it on a couche (well, I got a length of thick cotton table-cloth material from a textile shop and hemmed the edge).
I flipped it onto a polenta-dusted "peel" (actually the off-cut from the ceramic tile I used in my oven) and slid it directly on the hot tile. The bread Ballooned (?does this mean it was under-prooved?) and the top-being closest to the element, almost burned.