Place wax paper on cookie sheet; set aside. Bake potato then mash, should have approximately 3/4 cups. Mix together potato, vanilla and salt. Slowly add the cocoa and the powdered sugar. Beat till the mixture is stiff enough to be shaped into balls, approximately 1" in diameter. Refrigerate for two hours. Dip them into glaze one at a time while still cold. Let excess drip off and place on wax paper and refrigerate till chocolate is set. Store in refrigerator in a sealed container.
In top of double boiler over hot, not boiling, water melt chocolate and butter; stir till mixture is smooth. Cool slightly.