Add cake mix, oil and milk.
Mix for 4 minutes.
Put in greased and floured 11x15 cake pan or jelly roll pan.
Bake for 20 minutes in 325 degree oven.
Take out and let cool for 10 minutes.
TOPPING: While cake is baking and cooling, melt margrine and butter on low heat.
Once melted, add vanilla to butter margarine mixture and set aside.
In bowl, mix brown sugar and sugar first with wire whisk.
Add cinnamon and flour and use whisk to blend.
Add margrine/butter mixture to sugar/flour mixture and mix together with fork.
Do not mix too long or drumbs will be too fine.
Spread mixture across top of cake.
Bake for another 20 minutes.
Sprinkle top with confectioner's sugar.