Use 4 medium baking potatoes. Peel if desired. To prevent darkening, immerse peeled potatoes in a bowl of cold water until ready to cut. Use a food processor or rotary processor to slice potatoes into thin slices or use a potato peeler to slice into very thin slices. In a heavy, deep 3 quart saucepan or deep-fat fryer, heat shortening or cooking oil for deep fat frying to 375 degrees. To prevent splattering, pat potatoes dry. With a spoon carefully add potato slices a few at a time, to hot oil. Fry thin slices 4-5 minutes, very thin slices 3-4 minutes. Turn once. With a slotted spoon carefully remove potatoes from hot oil. Drain on paper towels. Keep potatoes hot in a 300 degree oven while frying remaining potatoes.