Melt butter in a large skillet over medium heat; add onion. Cook 10 minutes or until onion is tender and begins to brown, stirring often.
Cook broccoli according to package directions; drain well.
Cook chopped potato in boiling water to cover 10 minutes or until barely tender; drain.
Combine soup and next 6 ingredients in a large bowl, stirring well. Stir in onion, broccoli, potato, and ham.
Spoon ham mixture into a greased 3 1/2 quart casserole.
Unfold piecrust onto a lightly floured surface and press out fold lines. Roll pastr to extend 3/4 inch beyond edges of casserole. Place pastry over ham mixture. Seal edges, and crimp. Cut slits in top to allow steam to escape.
Bake, uncovered, at 400° for 45 minutes or until crust is golden.