Ingredient

Crème pâtissière

Pastry cream is custard with enough starch in it to stand up. Unlike a pouring custard it must be boiled — that is the one instruction people find counter-intuitive, and skipping it gives a cream that tastes of raw flour and goes runny in the fridge.

Why it is boiled

Cornflour thickens fully only once it has been brought to the boil, and egg yolk contains an enzyme that will break starch down and turn the cream to liquid overnight if it is not destroyed by heat. Boiling does both jobs at once.

The starch also protects the egg. In a pouring custard, boiling would curdle it; here the starch granules get between the proteins and prevent them linking too tightly, so a pastry cream tolerates a proper hard boil that a crème anglaise would not survive.

Boil it for a full minute or two after it thickens, stirring hard. Under-boiled pastry cream is the commonest fault and it shows up hours later.

Making it

1. Infuse the milk with vanilla, citrus peel or coffee if you want to, and bring it just to the boil.
2. Whisk the yolks, sugar and cornflour together into a smooth paste. Doing this thoroughly now is what prevents lumps later.
3. Pour a third of the hot milk onto the yolk mixture, whisking constantly, then return the whole lot to the pan.
4. Cook over a medium heat, whisking without pause and getting into the corners of the pan. It will thicken suddenly.
5. Once it bubbles, keep whisking for a further minute or two. It will look alarmingly thick — that is correct.
6. Beat in cold butter off the heat for gloss, then pass it through a sieve into a cold, wide dish.
7. Press cling film onto the surface and chill it fast. Spreading it thin cools it quicker and there is a genuine hygiene reason to get it cold promptly.

Variations worth knowing

Crème diplomate

Pastry cream folded with whipped cream. Lighter, less rich, and the best all-purpose tart filling.

Crème mousseline

Pastry cream beaten with a great deal of soft butter. Firm enough to pipe and hold; the filling in a proper fraisier.

Crème chiboust

Pastry cream folded with Italian meringue. Very light, and it must be used at once.

Chocolate

Stir chopped chocolate into the hot cream. Reduce the cornflour slightly, since cocoa butter firms it further on chilling.

Problems and fixes

• Lumps — the yolk paste was not smooth, or the whisking stopped. Sieve it; there is no shame in this and every professional does it.
• Runny the next day — under-boiled. The yolk enzyme has eaten the starch. It cannot be repaired.
• Tastes floury — under-boiled again, in the other direction. The starch never fully cooked out.
• Skin on top — cling film pressed onto the surface, not stretched over the bowl.
• Weeping after a day or two — normal syneresis, worse if it was frozen. Whisk it smooth before using.

Common questions