Before there were cake mixes, there was cake. But a surprising new book, "Something From the Oven" (Viking. $24.95), by food historian and former NEWSWEEK writer Laura Shapiro, reveals how the packaged-food industry, established in the 1950s to provide meals for soldiers in foxholes, worked tirelessly to convince American homemakers that processed foods were not only acceptable, but superior. It succeeded: after decades of eating boxed and frozen food, many Americans prefer artificial flavors to the real thing. But the desire to feed loved ones with food prepared "by our own hands," says Shapiro, is one thing that hasn't changed.