First preheat the oven to 350 F. Grease a baking pan and set aside.
Combine margarine, icing sugar, vanilla sugar, and vanilla extract in a mixing bowl, beat until fluffy in a medium speed.
Lower mixer speed, add in flour bits by bits, mix well. Spread batter in greased pan and bake for 18-20 minutes.
Meanwhile, combine eggs, sugar, orange rind and orange juice, stir to blend with spatula or wooden spoon, do NOT beat.
When cake is baked, take it out from the oven and pour the eggs mixture over the cake; return to oven and bake until topping is set (another 18-20 minutes).
Take out cake from the oven, wait until it is warm, then sprinkle evenly icing sugar on top.
When cool, cut squares and remove from baking pan, serve.