My husband doesn't like potatoes (go figure!) but he loves this casserole.
I boil a couple of large potatoes until a little before they're done. I use them with peel on for the roughage and flavor but you can peel if you want. Then slice them thinly without breaking (remember, he doesn't like potatoes) and spread over bottom of large casserole dish. Season with smoked salt and freshly ground black pepper. Then cover with chopped onions you've sauteed in some olive oil or some bacon grease. Then put some chopped cooked bacon on top. Then cover with a slight layer of grated extra sharp cheddar. Then repeat layers until you run out of goodies. Before putting it in a 350 degree oven, I then pour about 1 cup of heavy cream or half and half (the former is better but fattier, of course) into the pan and bake until fork goes in easily -- maybe 30 minutes. Each time you add a layer of potatoes, go ahead and re-season. You can also add garlic to the onions when you saute them, too.