Place the chocolate and margarine in a glass bowl and microwave for 30 seconds. Remove and stir and repeat this process one more time.

Separately, heat the cream over medium heat until simmering. Remove from the heat and pour over the melted chocolate mixture. With a rubber spatula, stir the chocolate until the mixture is smooth. Whisk in the vanilla extract.

Pour the chocolate mixture, called ganache, into a bowl and refrigerate, uncovered, for 1 hour. Using a melon baller or a teaspoon, scoop out the ganache and roll into balls with your hands. Place on a baking sheet lined with parchment paper and refrigerate for 30 minutes. Roll truffles in cocoa powder and serve or store.