Pastry cream and crème anglaise start from the same three things — egg yolks, milk, sugar — cooked over heat until they thicken. Only one of them can survive a full boil. Cornstarch is the difference. Pastry cream has it, and that starch lets the mixture heat past the point that would otherwise scramble the eggs, then set thick enough to hold its shape in a tart shell or an éclair. Crème anglaise skips the starch, so nothing protects the eggs once the temperature climbs. It has to come off the heat before the milk shows a single bubble.
Why crème anglaise curdles the moment it boils
Crème anglaise thickens by one mechanism only: the egg yolks' proteins unfold as they heat and link into a loose network that traps liquid, the same way any custard sauce thickens. That network is stable across a narrow band, roughly 170°F to 180°F (77°C to 82°C). Push past it and the proteins keep linking, tightening into a denser mesh that squeezes the trapped water back out. What was a smooth sauce a moment earlier is now grainy curds floating in a thin liquid — a boiled egg, essentially, suspended in milk. There's no starch, no backup thickener, nothing standing between the yolks and that failure point. The only real safeguard is a thermometer and a willingness to pull the pan early.
Why cornstarch lets pastry cream take the same heat and keep going
Cornstarch changes the chemistry entirely. As the mixture heats past about 203°F (95°C), the starch granules absorb water and swell into their own gel network — a second thickening system running alongside the eggs, not dependent on them. That network physically keeps the coagulating egg proteins spread apart instead of clumping into curds, so pastry cream can be brought to a full rolling boil without breaking. In fact it has to be. Raw egg yolks carry a small amount of alpha-amylase, an enzyme that breaks starch back down into simpler sugars. A minute or two at a hard boil denatures that enzyme. Skip it, and the amylase keeps working quietly in the fridge, digesting the very starch that thickened the cream, which is why an undercooked batch turns watery by the next day instead of holding.
The ratio each is built on
| Pastry cream | Crème anglaise | |
|---|---|---|
| Thickened by | Egg yolks + cornstarch | Egg yolks alone |
| Cooked to | A full boil, 200°F+ (93°C+) | 170–180°F (77–82°C), never boiling |
| Texture on cooling | Sets firm, holds a shape | Stays pourable indefinitely |
| Typical use | Filling for tarts, éclairs, doughnuts | Sauce, poured over a finished dessert |
Both run on roughly the same base ratio: about 2 egg yolks and 3 tablespoons of sugar per cup of milk. Pastry cream adds 2 tablespoons of cornstarch to that same cup; crème anglaise adds none. Because that ratio scales in parts rather than fixed amounts, doubling the milk means doubling everything else alongside it — including the cornstarch, if you're aiming for pastry cream's set rather than crème anglaise's pour.