Custard Sauce (Gills milk yolks of eggs)

A stirred custard sauce of the plainest kind, meant to be poured over baked puddings. The whole of the technique hangs on the one instruction the original gets wrong for modern equipment.

• Do not boil itYolk proteins begin to set well below the boil, and a milk custard thickens at around 175-180F and curdles not far above; milk boils at 212F. Held over direct heat at a boil, this sauce scrambles. Cook it gently, stirring constantly, until it coats the back of a spoon and a drawn finger leaves a clean track.
• GillsIn American measure a gill is half a cup, making 3 gills 1 1/2 cups (about 350 ml) of milk; in British measure a gill is 5 fl oz, which would give closer to 425 ml. Whole milk gives the right body; skimmed milk makes a thin sauce that needs an extra yolk.
• Temper the yolksBeat the yolks with the sugar and salt, then pour in the hot milk in a thin stream while whisking before returning everything to the pan. Adding cold yolks to hot milk is the other common route to curdling.
• Vanilla"A little vanilla" may well mean extract, for which about half a teaspoon suits this quantity. If using a vanilla bean instead, split it into the milk while it heats and remove it before adding the yolks.
• Strain and coolPour the finished sauce through a fine sieve into a cold bowl the moment it thickens; residual heat in the pan will keep cooking it. Stir occasionally as it cools to stop a skin forming.
• YieldAbout 1 3/4 cups, enough to sauce six modest servings of pudding. Serve warm or cold, and keep refrigerated no more than two days.
• If it breaksA sauce that has just begun to grain can sometimes be rescued by immediate blitzing with a stick blender or hard whisking off the heat. Once it is visibly scrambled, start again.