Heat 1/4 cup butter in a 9-inch skillet. Add onion and cook until lightly browned, stirring. Add beef, salt, pepper and savory and continue cooking 5 minutes longer. Stir in gravy and heat until bubbling. Spoon into a buttered 8-cup flat casserole dish.
Top meat mixture with mashed potatoes. Dot with pieces of butter. Bake at 400 degrees F for 15 to 20 minutes or until potatoes are lightly browned.