Put 1200 grams of water and margarine up to boil in a sauce pan over a medium heat. Just before it reaches a boil, slice open and scrap the vanilla pod, adding the contents to the pan. 

In a separate bowl, combine the sugar and starch.

Add the egg yolks and 60 grams (about 1/4 cup) of water to the sugar mixture. Whisk until combined.

Once the water reaches a boil, pour in the sugar and egg mixture. Whisk quickly until thickened.

Once thickened, remove from heat and pour from pan onto a baking sheet fully lined with plastic wrap. Wrap the plastic wrap tightly around the cream. Let rest in fridge or in a cool place for two hours before using. 

TO MAKE DIPLOMAT CREAM: Combine equal parts whipped topping and creme patisserie.