Melt butter in a large skillet over low heat; add oil and onions. Sauté over medium heat 15 minutes or until onions become slightly tender and lightly browned, stirring frequently. Remove from heat, and transfer to a 10- x 6- x 2-inch baking dish. Combine remaining ingredients, stirring well; pour over onions in dish.
Cover with aluminum foil; bake at 350° for 45 minutes or until onions are tender. Remove and discard bay leaf. Serve hot.