Chocolate Buttercream Prinzregenten Frosting

I wish I could give you an exact recipe for this frosting, because when I made it for this torte, it turned out amazing. Very rich, very chocolaty, and the perfect frosting for this torte if I do say so myself. I am not even sure is even I could duplicate this frosting, as I simply eyeballed amounts. However, I will try to give some guidelines to follow. It is nothing fancy or special, just simply delicious.

Ingredients
soft margarine
unsweetened cocoa powder
icing sugar
2% milk
vanilla

Put a little margarine in a small bowl, and mix in some cocoa. I used quite a bit of cocoa, because I really like chocolate. Use about a tablespoon or two of margarine, and as much cocoa as you can while still being able to stir the mixture. Stir in some icing sugar alternately with some milk, until you reach your desired amount or desired "shade" of icing. For example, for a darker chocolate flavor like I did, use a greater proportion of cocoa and less icing sugar. Stir in a splash of vanilla.

To assemble the torte: One cake layer, spread gently with a layer of frosting, repeat for all four layers. Pipe borders or rosettes around and on top of the cake if you wish. Heat a little additional frosting in the microwave briefly to warm it and thin it, then drizzle it over the cake.