peel potatoes and cut into medium cubes. cover with water in a pot and bring to a boil. boil until fork tender and drain. return potatoes to pot and place over low heat for a few seconds, until some of the water has evaporated. place cup of milk in microwave and heat for 1 minute. remove potatoes from heat and add butter, and mash with a potato masher, add milk until potatoes are smooth and virtually lump free. add salt and pepper to taste.
taking one hot dog at a time, make a cut all of the way down the length of the hot dog, not cutting all the way through, so that you can fold open the hot dog, and lay flat on a cookie sheet, cut side up. line all hot dogs up, and spoon mashed potatoes down the length of the cut open hot dog.
rip each slice of american cheese down the middle and lay the 2 pieces of cheese on each hot dog, on top of the mashed potatoes. when all hot dogs have cheese on them, place in the oven and bake until cheese is melted and barely browning on the edges. when ready, take out of the oven and serve.