When I confessed that I was finally ready to mail order cooking and baking supplies, Nancy Leson pretended to be surprised. "What?" she gasped. "You don't sit online all day and order things?" I've always avoided shopping cooking ingredients by mail because, just like the electric car I'd love to have, I could never get it to make any economic sense. The for-instance I gave Nancy was first clear flour, unobtainable in stores around here. It's traditional in old school New York deli rye. But at