METHOD: Put sugar, milk, condensed milk and butter into a large heavy saucepan. Cook over medium heat, stirring constantly until mixture reaches soft-ball stage (To test for soft-ball stage, drop a little into a cup of ice cold water. If it is firm enough to be molded into a soft ball then it has reached the required temp. of 116 degrees Celsius). Remove from heat, add smoothly mashed potato and beat with a rotary beater until all lumps are beaten out. Return to heat and cook to soft-ball stage once more. Remove from heat, stir in nuts, rose water and cardamom & mix well. Pour into a well buttered shallow dish or baking tin. Press lightly with a piece of buttered banana leaf or aluminum foil to smoothen and flatten the surface. Allow to cool and set, then cut into diamond shape.