1. Pour chocolate into a microwave-safe bowl. Heat in a microwave oven on half power (50%) until chocolate is soft, 2 to 2 1/2 minutes.
2. Meanwhile, in a blender combine tofu, rum, and vanilla. Whirl until smoothly puréed.
3. Stir chocolate until smooth. Scrape into blender with tofu mixture. Whirl until smoothly puréed. Pour into a bowl and nest in ice water. Stir often until frosting is cold, 10 to 12 minutes. Use or cover airtight and chill up to 2 days; stir before spreading.
Nutritional analysis per tablespoon.