Place the cream in a heat-proof bowl, and set the bowl over a pan of simmering water. Cook until heated through. Using a wire whisk, slowly stir the white chocolate into the warm cream until completely melted. Whisk in the liqueur and vanilla. Cover and chill for 1 hour or until pliable but firm enough to scoop. Preheat the oven to 350 degrees F. With 2 teaspoons or a 1 1/4-inch ice cream scoop, make dollops of the chocolate mixture and place on a baking sheet lined with parchment paper. Refrigerate for about 15 minutes, until firm enough to roll into rough spheres. Place the chopped hazelnuts on a sheet pan and place them in the oven for 8 minutes. Cool to room temperature. Melt the bittersweet chocolate in a heat-proof bowl, set over a pan of simmering water. Drizzle the melted bittersweet chocolate over 10 of the truffles. Roll the remaining truffles in the chopped nuts. Chill until ready to serve.
Note: This recipe has been updated and may differ from what was originally published or broadcast.