Cover a countertop area or large baking sheet with waxed or parchment paper.
In a medium mixing bowl, combine the mashed potatoes and butter, mixing well. Gradually add the sugar(s), blending until smooth. Stir in the vanilla extract and coconut; if the dough is too thick or won't hold together, add the milk or cream.
Roll into balls (about 1 inch in diameter) and put in the freezer for about an hour.
In a medium saucepan or double boiler, melt the chocolate morsels over low heat. Once melted, remove the truffles from the freezer and coat each one in chocolate, using a skewer or fork, tapping each against the side of the pan to drip off excess.
Transfer to your sheet of parchment or waxed paper; add sprinkles if you'd like them to have a decorative finish.