Pastry cream can be used as a filling for pies or tarts, cream puffs, eclairs, etc.

There are various schools of thought when it comes to the thickener: flour, cornstarch, or a mixture of the two.

1. Heat the milk with the split vanilla bean.
2. In a bowl, whisk the egg yolks with the sugar until pale and light. Gradually mix in the flour and cornstarch.
3. Thin the mixture by gradually mixing in half the milk. Add the remaining milk. It's important to do this gently to prevent the mixture from becoming foamy. 
4. Pour into a saucepan and gently bring to a boil, stirring constantly and scraping the sides of the pan with a spatula. Be very careful that the mixture doesn't stick to the bottom of the pan. Once the pastry cream has thickened, remove from the heat. If the pastry cream is still liquid, continuing cooking until very thick: it will thin out somewhat when cold. 
5. To prevent the formation of a skin, coat the surface of the pastry cream with a piece of butter while still hot; let cool; cover with plastic wrap and refrigerate until needed.