Ingredient

Custard

Custard is egg yolk and dairy persuaded to thicken without scrambling, and the whole difficulty is that the thing that thickens it is the same thing that ruins it. A degree or two either side of the right point is the difference between pouring cream and sweet scrambled egg.

The two custards

What most British kitchens call custard is a starch custard — cornflour, milk, sugar and usually a little colour and flavour. It is thickened by starch, it can be boiled hard without harm, and it is essentially foolproof. This is what comes out of a tin or a packet, and there is nothing wrong with it.

The other is a true egg custard, crème anglaise: yolks, sugar, milk or cream, and no starch at all. It is thickened purely by egg protein setting, which happens in a narrow band of temperature well below boiling. It tastes considerably better and it will split if you stop paying attention.

A great many recipes quietly hedge by adding a teaspoon of cornflour to an egg custard. This is not cheating — the starch physically gets between the egg proteins and makes curdling far harder — and if you are nervous, do it.

What is happening, and when

Temperatures here are about texture, not safety.

Below about 70°C

Nothing much. The mixture is thin and tastes of raw egg.

Around 76–80°C

The yolk proteins unfold and link loosely. The custard thickens and coats a spoon. This is where you want to stop.

Above about 85°C

The links tighten and squeeze out water. The custard goes grainy, then visibly scrambled, and it does not come back on its own.

Boiling

Fine for a cornflour custard, which needs a proper boil to thicken fully. Fatal for an egg one.

Making a pouring custard that works

The method is entirely about keeping the eggs away from direct heat.

1. Warm the milk or cream in a pan until it steams and small bubbles gather at the edge. Do not boil it.
2. Whisk the yolks and sugar together properly first, until noticeably paler. Sugar sitting on raw yolk will start to cook it.
3. Pour the hot milk onto the yolks slowly, whisking the whole time. This is the tempering step and it is the one that prevents disaster — you are raising the eggs gently rather than shocking them.
4. Return everything to the pan on a low heat and stir constantly with a spatula, getting into the corners. Stop stirring and the base cooks first.
5. Take it off the heat the moment it coats the back of a spoon thickly enough that a finger drawn through leaves a clean line. It thickens further as it cools.
6. Pour it straight into a cold bowl through a sieve. The sieve catches any strands that did set, and the cold bowl stops the cooking.

Rescuing a split custard

Act immediately — this works while it is still hot and gets less effective by the minute.

• Take it off the heat at once and tip it into a cold bowl to stop it cooking further.
• Blend it hard with a stick blender. Curdling is protein clumping, and shearing the clumps back into suspension genuinely repairs a mildly split custard.
• If a blender is not to hand, whisk violently, then push it through a fine sieve. The result is thinner but perfectly pleasant.
• If it is properly scrambled — visibly lumpy, smelling of omelette — it is finished. No amount of blending brings that back.
• Full diagnosis on the curdled custard page.

Using it

• Pouring — the loosest, straight over a pudding. Stop it early, at barely coating.
• Baked — as in a tart or a crème brûlée, where the whole thing is set gently in the oven rather than on the hob. A water bath moderates the heat.
• Ice cream base — a slightly richer custard, chilled thoroughly before churning.
• Crème pâtissière — a much thicker, starch-stabilised custard for filling tarts and buns. See crème pâtissière.
• Left over — a skin forms as the surface dries. Press cling film onto the surface itself, not across the bowl.

Common questions