Invert ice cream bombe onto wire rack over rimmed baking sheet. Remove bowl and plastic wrap. Melt remaining chocolate according to package directions. Pour melted chocolate over bombe, using a spatula to evenly coat. Run a fork over outside of ice cream bombe starting from the top of the dome down and repeat along entire outer coating to make decorative lines all around bombe. Transfer to serving plate; return to freezer. Sprinkle with icing sugar just before serving.