-ORsemisweet chocolate -chopped Bring whipping cream and unsalted butter to simmer in heavy medium saucepan. Reduce heat to low. Add half pound bittersweet chocolate and stir until melted. Mix in 2 tablespoons Cognac. Let stand at room temperature until firm enough to mound on spoon, about 3- half hours. Line cookie sheet with foil. Spoon truffle mixture by rounded tablespoons onto prepared cookie sheet, spacing apart. Chill until firm, about 1 hour. Roll 1 truffle between palms of hands into ball. Place on same sheet. Repeat with remaining truffles; refrigerate. Melt 0.75 pound chocolate in top of double boiler over simmering water, stirring frequently until smooth. Remove from over water. Grasp 1 truffle between thumb and index finger. Dip into chocolate, coating completely. Shake gently to remove excess chocolate. Place on same sheet. Repeat dipping with remaining truffles. Refrigerate until firm, about 30 minutes. Remove truffles from foil. (Can be prepared 1 week ahead. Refrigerate in airtight container.) Serve cold.