Preheat oven to 375 degrees. Grease and flour a jellyroll pan.
In a saucepan over medium high heat combine margarine, water and cocoa. Bring to boil, then add sugar, flour and baking soda. Using a mixer combine and add the eggs and sour cream. Pour batter into prepared jellyroll pan and bake in preheated oven from 15 to 20 minutes. Remove from oven and frost immediately.
To make frosting: In a saucepan, combine all frosting ingredients except powdered sugar. Bring to boil, remove from heat and add powdered sugar. Using a mixer, beat frosting until smooth and creamy. Add vanilla and beat until blended. Frost hot cake and let cool immediately. Cool cake in pan or wire rack until completely cooled. Cut into squares. May decorate each square and place in scuffle papers. Makes 4 dozen squares. Enjoy!