Melt butter in small skillet over medium heat; add onion and sauté until tender, about 5 minutes, stirring constantly. Flake ham chunks into large bowl. Stir in onion. Add beaten egg, bread crumbs and grated cheese. Mix well. Place mixture in lightly greased 9 x 5 x 3-inch loaf pan. Bake at 350 degrees for 30 minutes.