"On Second Thought" continues its "Main Ingredient" series in which a chef tells us about his or her essential Southern ingredient. For Chef Virginia Willis , that's the pear — her favorite fall fruit . Willis, who is also the author of cookbooks including " Lighten Up, Y'all ," grew up around her grandparents' pear tree. She invited us into her kitchen for a lesson on how to make pear mostarda and black pepper cream cheese biscuits. Both recipes are in her newest cookbook, " Secrets of the