Lay the slices flat and using a round cookie cutter or a spoon, remove most of the insides. Leave a very thin rim of potato around the edge for structure. As you go, dump the insides into the bowl of your mixer with the butter and sour cream.
Let the potatoes cool a bit so that you can slice them. Cut off the end pieces from each potatoes then slice each in about 4 equal slices, mine were about 1 inch or a bit less in thickness.
Preheat oven to 375 F degrees. Place the potatoes on a baking sheet and bake for 1 hour to 1 hour and 30 minutes, or until the potatoes are tender and the skins are slightly crisp.