• Line a 9 x 9 inch pan with waxed paper.
  • In a medium-sized saucepan, bring whipping cream and vanilla almost to a boil. Remove from heat, cover and set aside 30 minutes.
  • In a small bowl, whisk sugar and egg yolk until pale and thick, then whisk into whipping cream and vanilla mixture in saucepan.
  • Return pan to heat and gently heat without boiling. Add chocolate, espresso and butter. Stir until mixture is smooth. Stir in crème de cacao.
  • Pour into lined pan and chill 1 hour or until firm. Spoon out pieces of chilled truffle mixture and roll into balls.
  • To prepare coating, sift cocoa and powdered sugar onto a plate. Roll each ball in sifted cocoa mixture and place in paper cup, if desired. Refrigerate and eat within 2 to 3 days.