6 ounces dark chocolate, finely chopped
1/2 cup heavy cream
1/2 cup mashed ripe banana (from about 1 small banana)
1/2 teaspoon vanilla extract
8 ounces chopped dark chocolate or chocolate candy coating, finely chopped
1-2 teaspoons unflavored vegetable shortening or cocoa butter, optional
Line an 8-inch-round cake pan with aluminum foil or plastic wrap. Place finely chopped chocolate in a heat-proof bowl.
Warm cream in a saucepan over low heat until it starts to steam (do not let it boil). Pour cream over chocolate; let sit for 30 seconds and then stir until smooth.
Pour chocolate mixture into a food processor and add banana. Pulse until smooth. Stir in vanilla. Pour into prepared cake pan. Press a piece of plastic wrap down onto the surface, smoothing out the top as much as possible. Refrigerate until set, at least 4 hours or overnight.
Remove pan from refrigerator. Gently lift the chocolate out of the pan using the plastic wrap or foil and carefully peel away top layer. Using a 3/4-inch round cookie cutter, cut rounds of filling from block. Arrange on a parchment lined baking sheet. Scraps can be rolled into balls. Refrigerate until ready to use, or freeze for 15 to 20 minutes.
Meanwhile, gently melt chocolate or candy coating, taking care not to overheat the chocolate. If desired, add a little vegetable shortening to thin out the chocolate a bit. If you can manage to keep the chocolate under 88 degrees, it should retain its temper. You can also use the seed method if you like. Otherwise the truffles will need to be refrigerated to retain their hard shells.
Using a fork or dipping tool, dip each truffle into the melted chocolate, tapping off any excess. Place dipped truffles on a second parchment-lined baking sheet. Top with sprinkles or decorations, if desired, before chocolate has a chance to harden.
Store truffles, refrigerated in an airtight container, for up to a week.