Pastry cream is staple in many pastry kitchens. It is often used to fill cakes, tarts, and pastries like pate a choux, napoleons, croissants and Danish. It is a cooked, stirred custard, which is defined as a custard cooked on the stove top with constant agitation. The main ingredients of pastry cream are milk, egg yolks, sugar and cornstarch. Unlike crème Anglaise, pastry cream contains cornstarch, which swells during cooking and thickens the cream.
There are several critical steps in making of pastry cream.
1. Whisk together cornstarch and remaining sugar (or second portion of sugar) first, then add egg yolks.
Otherwise, the cornstarch will form lumps that will not dissolve into the cream during the cooking process.
2. Do not allow the egg yolks to sit on the starch / sugar mixture.
The yolks may “burn” where there is contact with the starch / sugar mixture, forming a thick skin that will not dissolve into the cream.
3. Temper hot milk into yolk / starch / sugar mixture
Gradually add the hot milk into the yolk mixture while whisking. By raising the temperature of the egg yolk mixture gradually, curdling of the egg protein is prevented
4. Return to the stovetop. Constantly whisk while cooking over a medium high heat
It is critical to stir the bottom and the sides of the pot during the cooking process to avoid scorching. A wire whisk should be used instead of a rubber spatula. The mixture will thicken very quickly, and a whisk helps to stir the cream into a smooth texture.
5. Bring to a boil and maintain the boil for minimum of 2 minutes
After the first sign of boiling occurs, the cream should be kept boiling for the next two minutes. This ensures to fully swell the starch and thicken the texture. If the cream did not (cook long enough) have enough cooking time, it will result in a runny texture and starchy flavor.
6. Cool as quickly as possible
After cooking, the cream should be deposited onto a clean, shallow container and spread thinly. The cream should be covered to the surface with plastic wrap to prevent a skin from forming.
Because pastry cream has a high moisture content and perishable ingredients, it is advised to store under refrigeration and use as quickly as possible. If the cream is used fresh, for example in fresh fruit tarts and in eclairs, the shelf life is no more than 2 days after making of the cream. If it is being baked as a component of Danish or rustic tarts, then shelf life is 5 days. Pastry cream cannot be frozen because gelled starch breaks down during the freezing and thawing process. The cream will weep moisture, and it will not have the same consistency as it had before freezing.
Pastry cream can become a base for various other creams, such as diplomat cream (with crème Chantilly folded in), crème mousseline (whipped with softened butter), and frangipane (combined with almond cream). It can also be flavored as desired. Depending on the flavoring agents, they may be added at different steps throughout the process. Items like spices and tea should be infused into milk and strained out before the cooking process. Chocolate can be added at the end of the cooking process, so that the heat of the cream can melt the chocolate. Any alcohol based flavorings like extracts and liquors should be added once the cream is cooled, to prevent the flavor from evaporating with heat. Extracts without alcohol and nut pastes like praline paste can be added either when the cream is hot or cooled.