Make ganache. In a double boiler, bring the cream to a simmer. Remove from heat and add chocolate. Let sit for 2 to 3 minutes. Whisk until well-blended, smooth and shiny. Add peppermint extract and whisk gently to blend.
Pour ganache into a shallow bowl. Refrigerate until nearly firm, about 2 hours.
Remove bowl from refrigerator. Ganache should be slightly soft and easy to handle. Scoop teaspoon-sized pieces and shape into balls with palms of your hands. Roll in sifted cocoa powder. Place in covered container and store in refrigerator. Let truffles warm to room temperature before serving.