For truffle base: Bring cream to simmer in heavy small saucepan.
Remove from heat; cool to lukewarm, 10 minutes.
Meanwhile, stir 7 ounces chocolate in metal bowl over saucepan of simmering water until smooth.
Remove from heat.
Add 2 ounces chocolate; stir until smooth.
Stir in cream.
Chill truffle base until firm enough to roll, about 3 hours.
Line rimmed baking sheet with waxed paper.
Roll 2 teaspoons truffle base between fingertips into ball.
Transfer to prepared sheet.
Repeat with remaining truffle base.
Chill until firm, about 1 hour.
For chocolate coating: line another rimmed baking sheet with waxed paper.
Stir chocolate in metal bowl over saucepan of simmering water just until melted.
Remove from heat.
Cool slightly.
Scoop some of warm (not hot) melted chocolate into palm of hand.
Place 1 chilled truffle in hand and roll in palm to coat.
Transfer to prepared sheet.
Repeat with remaining melted chocolate and truffles, rewarming chocolate if necessary.
Roll in cocoa powder if desired.
FOR variations, see page 61 for instructions on rolling in toppings.
Chill until firm, about 1 hour, do ahead can be made 1 week ahead.
Store in airtight container and keep chilled.
Let stand at room temperature 1 hour before serving.