In a 8"x8" baking dish, coat it with 1 tablespoon of butter; set aside. Slice the potatoes thin, peeled or not is your choice, and place half of them in a loose layer on the bottom of the baking dish. Sprinkle with some scallions. Repeat with another layer of potatoes and scallions. Sprinkle with the bacon bits, salt, and pepper to taste. In a medium saucepan, melt the butter. Add the flour and whisk for about a minute. Add the milk and stir until thickened. Add the cheese and stir until thickened, about 30 seconds. Remove from heat and gently pour over the potatoes. Loosely cover the dish with aluminum foil. PPC-XL: Place the rack in the bottom of the pressure cooker. Add 1 1/2 cups of water. Place the baking dish on the rack. Put the lid on the cooker and make sure the vent is set to pressure/closed. Press the Meat/Chicken button and then the Time Adjust button once to get a total time of 40 minutes. When the timer goes off, let the pressure release naturally. Carefully, remove the baking dish and let it set for about 5 minutes. Top with extra cheese, scallions, and bacon bits if desired. Serve hot.