To make custard sauce we carefully cooked a mixture of dairy, sugar, and egg yolks over a double boiler so that the yolks thickened but didn’t curdle, which only occurs within a very narrow band of temperatures around 80°C. It was nerve-racking.
It turns out that if you add starch to the mix, the eggs will never curdle, even if you boil the custard vigorously. The starch granules absorb heat, protecting the egg proteins, and the dissolved starch interferes with protein linking. Of course, the starch also thickens the custard, so you end up with something that is more like pudding than sauce.
This preparation is called pastry cream, or crème pâtissière, and it begins exactly as crème anglaise: in fact the recipes are almost identical. The only difference is that once the starch, usually cornstarch, is added, the custard can be cooked in a pot on the stove, instead of a double boiler. Unlike custard sauce, pastry cream should be brought to a simmer to let the starch cook out. Typically some butter is also beaten into the custard after it is removed from the heat.
When I make pastry cream there are usually some tiny clumps in it when I’m finished. I’m pretty sure these are rogue egg whites that have snuck into my custard by hiding on the surface of the yolks. You can press the custard through a fine wire sieve to remove these curds.
There are several fancy uses for this custard, most notably as a filling for pastries like doughnuts (think Boston cream) and éclairs. I would like to vouch for this preparation as something that can be eaten as pudding, in conjunction with stewed fruit and oatmeal crumble.
Master Ratio – 4 : 1 : 1 dairy, sugar, egg yolk plus corn starch and butter
- 4 oz heavy cream
- 4 oz whole milk
- 1 tsp vanilla paste
- 2 oz granulated sugar
- 2 oz egg yolk
- 0.5 oz cornstarch + 2 oz whole milk to make a slurry
- 1 oz unsalted butter
- Heat the dairy on the stove with the vanilla paste.
- Meanwhile, whisk together the egg yolks and sugar.
- Once the dairy simmers, remove it from the heat and temper the egg yolks mixture. Return to the stove and add the cornstarch slurry. Continue to whisk over medium-high heat until the custard thickens, then simmer gently for another two minutes to cook out the cornstarch.
- Remove the custard from the heat and slow the cooking either by using an ice bath, or by simply transferring the custard to a bowl.
- Whisk in the butter.
- Press the pastry cream through a fine mesh sieve to remove any bits of curdled egg white.
- Press plastic wrap onto the surface of the pastry cream to prevent the formation of a dry skin.