I call these lazy because who has time to actually peel the potato skins off. Using a mandolin on the medium setting (mine is #2 for thickness), slice your potatoes and onion. Lightly grease a 9x13 pan and lay does a layer of potatoe slices, followed by some onion slices, and repeat. I did this until I had 5-6 layers of potatoes. Next, melt your butter over medium heat. After melted, add the salt/pepper and flour and cook for 1 minute. Add in your milk, stirring so your flour mixture dissolves. Lightly stir until your mixture thickens, feel free to add additional flour if needed. After it thickens, stir in the cheese until the mixture is combined. Remove from heat and then pour it over the potatoes. You might need to use a fork to move the potatoes a bit so the cheese makes it way to the bottom. Cover the top with foil and put in the oven on 400 for 90 minutes. Because it’s a very full pan, place a cookie sheet under it to catch and cheese that boils over. It will looking runny as it’s cooking but it will solidify as it cools.