Cover potato cubes with water in saucepan and simmer until tender. Meanwhile, in large skillet, saute hamburger with onion until meat is browned and onion is translucent; drain. Add soup, can of corn, drained, 1/2 tsp salt, 1/4 tsp pepper to meat mixture and mix well. Pour into 2 quart casserole.
Drain potatoes, add butter, 1/2 tsp salt and 1/4 tsp pepper. Mash while adding evaporated milk, a little at a time, until they are mashed and smooth (it may not take the whole can of milk).
Spread mashed potatoes over the top of the meat mixture, making sure to get all the way to the edges. Sprinkle cheese over top. Bake 30-40 minutes until hot and bubbly.