Preheat the oven to 375°F.Combine all the ingredients except the onions and breadcrumbs in a small saucepan. Heat gently, stirring, until all are smoothly blended. Remove from the heat.Peel the outer skin from the onions and cut them in half crosswise. Cut a thin sliver from the bottom of each onion half, so that they'll stand steadily in a baking dish.Arrange the onions halves in a shallow baking dish and pour the mixture from the saucepan evenly over them.Cover and bake for 45 minutes to 1 hour, or until the onions are tender when pierced with a fork. Once or twice during this time, spoon some of the liquid from the bottom of the baking dish over the onions.Sprinkle the onions with breadcrumbs and bake, uncovered, for an additional 10 to 15 minutes, or until most of the liquid has been absorbed. Serve at once or keep warm until needed.