1 cup margaraine
2 cups sugar
1 tsp vanilla
1 tsp water ( if needed)
I just followed the same method for making the buttercream as I do with shortening or butter. Beat the margaraine which is at room temperature on a slow speed. Gradually add the sugar and beat on medium to high speed till the cream becomes light and fluffy. You can add the vanilla when you are adding the sugar. If you think the mixture is too solid or thick in consistency you can add 1 tsp water and then beat it again. You can add the water till you reach the desired consistency.
For assembling the cake, frost the buttercream over the chocolate cake. Use the oreo chocolate cookies for garnishing. I had cut them into halves and also crushed some of them to garnish the cake.