I'm the queen of casseroles, a self-assigned title, but it fits. Casseroles feel good. They are a good way to pack a lot of food in an easy package. They can be made ahead. Baked by others. They usually make good left overs. I like casseroles. This is an original recipe that has evolved over time.
Meanwhile, a scallion peeled and diced and two or three garlic cloves, minced or finely diced. Brown a pound of the best ground beef you can find with the onion and garlic. I was simply clueless how much better ground beef can be than the kind you buy at the grocery store. It's been night and day. If you are not buying local beef from a butcher who can tell you where it came from and that it was grown all natural, you won't regret the time to find it. Drain any liquid from the meat if necessary now.
Somewhere around 8 or so cleaned and quartered mushrooms. A can of green bean beans, drained. 1T. Worcestershire sauce. 4 or 5 T. ketchup. 1/2 C. beef broth. Stir and cook for a few minutes to combine the ingredients and to soften the mushrooms.
When the potatoes are soft, drain them and return them to the pan. Mash them with a potato masher. Add butter and cream and salt as if making mashed potatoes. Your decision how rich, but I recommend living a little.
The meat mixture into a casserole. The potatoes over top.