In a medium mixing bowl, combine cold mashed potatoes with salt and vanilla. Add icing sugar, one cup at a time, beating after each addition. At first the mixture will be stiff and hard to handle but with beating it will become very runny. With the addition of the fourth cup, the mixture will firm up again. Turn half of the mixture on to a board that's been lightly dusted with icing; roll into a rectangle two inches thick. Spread with half of the peanut butter. Roll up from the short side, jelly-roll fashion. Repeat with rest of fondant. Refrigerate until firm; slice 1 cm thick. Makes 4 dozen candies. From The Gazette, 45. 0.18518518518519.