Line an 8-inch square baking pan with nonstick foil, leaving a small overhang on two sides. Line a large baking sheet with waxed paper. Heat cream and liqueur in a small saucepan just to simmer.Advertisement
Process chocolates and confectioners sugar in food processor 1 to 2 minutes, until finely chopped. With machine running, add cream-liqueur mixture in steady stream. Process until smooth. Scrape into foil-lined pan. Refrigerate just until thick enough to hold shape, 1 to 1-1/2 hours.
Lift chocolate from pan using foil. Cut chocolate into 36 pieces. With hands, quickly shape into balls. Place on waxed-paper-lined baking sheet. Refrigerate 15 minutes. Reroll truffles to smooth out surface, if needed.
Sift cocoa into small bowl. Add truffles, three at a time; tossing to coat. Refrigerate in airtight containers up to 1 month, placing each in a small paper or foil candy cup, if desired. Note: Look for paper candy cups at confectioneryhouse.com.