Cut chocolate and margarine into small pieces.
Heat the cream till it comes to a boil, stirring constantly.
Pour the boiling cream over the chocolate pieces and margarine. Wait a few minutes, allowing the hot cream to melt the chocolate.
Add the cocoa and mix well (caution: do not overwork the ganache).
If you plan to add other ingredients for flavor, do so now.
Transfer the mixture to the refrigerator and allow it to harden for approximately four hours.
Form the hardened ganache into small balls and place them on wax paper.
Use a double boiler to melt some more chocolate.
Stick a fork or skewer into one of the ganache balls, and dip it onto the melted chocolate.
Remove from the chocolate and roll in the coating of your choice. Alternatively, you can let the chocolate coating harden, and then drizzle the truffle with a contrasting color of chocolate.
Repeat for the remaining balls. Place completed truffles inside candy-size cupcake holders.
The chocolates will keep wrapped tightly in the freezer, enabling you to get a head-start on your Purim preparations.