First, clarify some butter. I did this the day before. I only clarified a half pound. Just toss some butter sticks in a pot on the lowest possible stove setting. When it is all melted, spoon off the top foam (and keep it as a flavorer for popcorn or potatoes), then pour the center clarified butter into a storage container. On the bottom will be some white milk solids, and I don't know what they're good for. It may be easier to separate the layers if they are cooled and solidified, but I didn't do that. The reason to clarify butter is that it raises the smoking point by about a hundred degrees F, so you can cook things in butter at higher temperatures without burning it. It also removes a lot of lactose, which you care about if you're lactose-intolerant.
2 lbs white potatoes (Yukon golds, whatever)- ~$1.20
4 Tbsp melted clarified butter - ~$0.35
salt, pepper, garlic powder - $0.05
Slice the potatoes into 1/8" slices (just eyeball it or use a machine). Preheat your oven to 450 F. Use about a third of the butter to coat the bottom of a cast iron skillet. Put down potato slices in concentric rings or a spiral in the skillet, slightly overlapping or not. Brush with butter, then sprinkle with salt, pepper and garlic powder. Repeat layers of potato/butter/seasoning until you are out of potato. Pour on any remaining butter.
This is a great side dish for six for about $1.60 and 1000 calories, or about $0.27 and 170 calories per person. Very tasty. Do NOT put ketchup on this. It's great how it is, which is covered in butter.
The original recipe called for 4 medium potatoes in an 8" skillet for 30-35 minutes, but I used 4 enormous potatoes in a 12" skillet, and mine took twice as long. The original also said to have the lid on, but this trapped so much steam from the potatoes that dripped back down that they were getting a little mushy instead of crispy, so I took the lid off.