Medrich's Cocolat (not reviewed) was a lavish collection of heart-stopping (in both senses) desserts. Does this assemblage of low-fat sweets (in most, less than 30% of the calories come from fat) mean she is lowering her decadent standards? Don't bet on it. As she sensibly points out in the introduction, changes in our eating habits have affected our palates too: These days, food with less fat just tastes better. Someone comparing her dense brownies made with unsweetened cocoa to standard brownies would probably note a difference without necessarily preferring one over the other. Mostly Medrich has skipped the losing battle of substitutions and makeovers (one exception, tiramisÃ¹ with a cottage and cream cheese mixture in place of mascarpone, is sacrilegious). Instead, she's come up with a whole range of ingenious techniques -- from freezing mousses to make them fuller-tasting to adding doses of acidic dairy products to tenderize baked goods -- to create a range of original sweets. Frozen hot chocolate with low-fat milk is a snap, while a chocolate cake with three kinds of mousse takes over two hours to prepare. A final chapter gives recipes for new, low-fat versions of basics like pastry creams so that readers can try working Medrich's magic on their own favorites. Two quibbles: A fair number of non-chocolate options make the title misleading, and fussy old-fashioned tableware lends photographs the ambiance of Great-Aunt Martha's dining room. A toothsome revolution.