Slice the potatoes thinly, the thinner the potatoes the faster it will cook.
Cut the Kielbasa into bite sized pieces.
In a casserole dish create layers. Start with the potatoes, then slice the butter and spread slices out, sprinkle flour over and salt and power then spread some Kielbasa bites out. I usually make 3 or 4 layers, but it can depend on how big your casserole dish is.
Pour milk into the dish, it will settle at the bottom.
Cover dish with foil and put in the oven.
Bake for 1 hr 30 minute or until the potatoes are fully cooked.