- Melt the chocolate in the microwave on low power, pausing to stir it every 20 seconds. (Alternatively, you can melt it gently in a double boiler set over a pan of barely simmering water.)
- Stir the sour cream into the chocolate, mixing vigorously to blend.
- Add the peppermint extract a bit at a time until you have achieved the desired flavor.
- Place the truffle mixture in a pastry bag fitted with a star tip and pipe rosettes on a foil or parchment-lined baking sheet. Refrigerate for 30 to 60 minutes, until firm, then place the truffles in paper candy cups.
- The truffles can be prepared up to two days ahead and stored in the fridge in an airtight container.
Note: If you don't want to use a pastry bag, you can spoon small mounds of the truffle mixture onto the baking sheet, then roll them into smooth balls after chilling. For a pretty finish, roll the balls in powdered sugar or cocoa powder before placing them in paper candy cups.