If you think novelists do research only in libraries, think again. Culinary mystery writer Diane Mott Davidson has a different approach: She caters. Far-fetched? Not when your perennial protagonist is one Goldy Schulz, a caterer who has cooked her way through such delicious mysteries as Dying for Chocolate and Killer Pancake, stories that include the author's own enticing recipes and mentions of cranberry and orange, both significant flavors in her comfort-dessert memory file. My husband was in the Navy and was often away at sea, so there was little opportunity to cook, she says. One day I was with some Navy wives, and somebody set out a cranberry-orange bread. I raved about it. Not long after that, I drove to Norfolk to meet my husband's ship, and stayed with the woman who had baked the bread. While I was there, she slipped another loaf of it into my suitcase. It was the nicest thing anybody could have done. Prepare the cranberry glaze for this lovely orange layer cake a day ahead to allow it to firm up and chill. And consider presenting the finished cake as a gift; you're sure to make someone's day.