In a heavy pot or sauce pan, over slow heat,  warm 1-1/2 cup milk and vanilla. 

In the meantime, put egg yolks in the medium size bowl and lightly whisk to break them. Combine flour and sugar together and strain into the bowl, whisking gently, and making sure that no lumps form. Whisk in the remaining half cup of cold milk, keeping a wary eye for lumps.

By this time the milk on the stove will be about ready to boil. Slowly whisk the hot milk into the egg-and-milk mixture. 

Return the cream to the pot and continue cooking over a low flame, stirring gently, until it barely reaches a slow boil (about 2 minutes). 

Transfer cream immediately to a bowl and let it cool, gently stirring it often to keep a skin from forming across top.
 

NOTE: This cream is one of the basic ingredients used in many Italian desserts and they would not be quite the same without it. Use it between layers of any sponge cake, as icing, in pudding or in the any fruit crostata. Just expand or reduce quantities as you need.

TIPS:
If you can, use round-bottomed heavy pot because its entire contents will be accessible to the spoon or whisk.

Crema Pasticcera should be transferred to a bowl as soon as it is ready, othervise it will continue to cook in the pot.

Instead of vanilla sugar or vanilla extract, use vanilla bean. Soak the bean in warm milk for about 15 minutes before cooking, cook the cream and remove vanilla bean when cream is ready. 

You could also flavor this basic Crema Pasticcera with other things (like couple coffee beans, melted chocolate or 1 tsp. of lemon zest), depending upon what you are going to use the cream for.