Single Ingredient Co0kbooks Beginning with Snacks and Appetizers and moving confidently through Sandwiches, Soups, Salads, Main Dishes, Breads and Desserts, Mable Hoffman expands the repertory of the standard jar of Skippy, Smucker's or Jif. The Peanut Butter Cookbook contains exotic concoctions (Teriyaki Shrimp & Vegetable Pizza) as well as down-home favorites (Peanut Butter Brittle), but in every case, the ingredients are accessible and the preparation is easy. (Berkley/HPBooks, $11 paper 128p ISBN 1-55788-243-6; July) Stealing the limelight from the perennially lauded apple, Pears by Linda West Eckhardt (Bread in Half the Time) offers 60 recipes for pears, including such variations as Pear and Chicken Picnic Salad, Bosc Tarte Tatin and Pear Kuchen. Tips on buying, ripening and cooking pears, with advice on which type is best for which purpose, precede the recipes; 120 color photos by Karl Petzke. (Chronicle, $16.95 paper 132p ISBN 0-8118-0668-5; June) Health Advice Walking for physical health has become this country's most popular exercise. In The Long Road Leads to Joy: A Guide to Walking Meditation, Buddhist monk and peace activist Thich Nhat Hanh illuminates the spiritual benefits afforded by walking mindfully. Encouraging his readers to walk with their attention on the present and gently to resist struggling with issues of the past or problems of the future, the author offers short meditative verses and personal observations to facilitate the practice of "walking peacefully." BOMC/One Spirit selection. (Parallax Press, $8 84p ISBN 0-938077-83-X; July) In Sharks Still Don't Get Cancer: The Continuing Story of Shark Cartilage Therapy, Dr. I. William Lane, the leading proponent of shark cartilage as a weapon in the fight against cancer, continues the controversial study disclosed in his 1992 book Sharks Don't Get Cancer. He updates readers on recent developments, including his experiences with the media, the medical community and government agencies. Writing with Linda Comac, he also answers the questions people most often ask about shark cartilage treatment. (Avery, $12.95 paper 248p ISBN 0-89529-722-1; J