Preheat oven to 350 degrees F. Peel, core, and slice three large pears; saute in hot butter until softened. Arrange pears in a greased 3-quart rectangular baking dish. Sprinkle pears with sugar, ground cinnamon, and dried cranberries or raisins. Top with panettone, tearing to fit. In a medium bowl whisk together eggs, eggnog (or half-and-half or light cream plus sugar) and vanilla. Pour over panettone in dish; press down lightly with the back of a spatula or large spoon to moisten all the bread. Bake, uncovered, for 35 minutes or until egg portion appears set. Let stand for 20 to 30 minutes before serving. Sprinkle with powdered sugar; serve warm. If desired, sprinkle with additional dried cranberries. Makes 6 to 8 servings.