line a small baking sheet or plate with parchment or waxed paper.
In a medium bowl, mash the sweet potato, then stir in the powdered sugar, coconut and vanilla.
Scoop in 1 tablespoon-sized portions, place on prepared pan. Refrigerate, uncovered, overnight.
The next day, neaten up the scoops of filling, pressing in any stray bits of coconut. Line a plate or pan with waxed paper for the dipped chocolates.
In a double boiler, bring water to a boil, then turn off the heat. Place the chopped chocolate in the upper pan, then cover and let stand for a couple of minutes, then stir with a heat-safe spatula. When melted, place the chocolate pan on a folded towel.
Drop each portion of filling in the melted chocolate, turn to coat, then use a fork to lift the candy out of the chocolate, tapping on the side of the pan to let excess chocolate drop into the pan. Place on the prepared pan. Coat remaining candies.
If desired, sprinkle with dragees or other decorations while the chocolate is still soft.
Chill until the chocolate is firm, then store in a covered container in the refrigerator until time to serve.