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In the end it looks like this.
Principle
Pastry cream is a custard variant like crème anglaise but thickened with flour. It’s made with flour, sugar, egg yolks, milk and, most of the time, vanilla. It’s used in multiple pastries (eg custard pie, strawberries tart, …).
Quite simple to make, it just requires the cook to be active all the time.
Ingredients (for 4 persons)
- 4 egg yolks
- 100 g of sugar (if you plan on adding vanilla, you can use vanilla flavoured sugar to increase the vanilla flavour in the cream - I personally have a full pot of vanilla-flavoured sugar: I put my empty vanilla pods in the pot with suger)
- 68 g of flour
- 44 cl of milk
- 24 cl of fresh liquid cream
Optional (depending on what you wanna do):
- 1 vanilla pod (or vanilla powder or vanilla aroma)
- some pistachio paste
- Pastry chocolate or cocoa
Preparation
Add the cream to the milk and put it to boil in a saucepan. If you intent to put vanilla, do it. If you have a pod, then slice it in two, extract its content and put it in the milk. If you wish to make vanilla-flavoured sugar, don’t put the empty pod into the milk. If not, you can add it to infuse it.

I added vanilla, because I love it.
Note
Milk tends to boil around 95°C
.
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Beware, hot.
Meanwhile, mix the sugar and yolks into a sabayon (meaning, mix them until the mixture becomes whiter, of course it won’t become really white, but it’ll get close to it) in a bowl. You need to whip the mix all the time otherwise the sugar may cook the yolks, altering the taste of the result.

Whitened sabayon.
As soon as the milk/cream mix starts to boil, remove the saucepan from the heat and extract the potential vanilla pots. Add half of the milk/cream mix to the sabayon.

Milk added to the sabayon.
Whip the mix to homogenize it.

News at 00:00, when homogenized, the mix looks better.
Put the resulting mix back in the saucepan and put it again on the heat. Keep whipping the mix. It’ll thicken in less than a minute. As soon as some bubbles pop, remove the saucepan from the heat and put its content in the bowl again. If you have pistachio or chocolate to add, now is the right time. (if it’s chocolate, melt it before, if it’s cocoa, then just add it as it’s)

Looks nice eh?
Enjoy!