Brandy Sauce

A foamy custard sauce for steamed and boiled puddings, thickened over hot water rather than direct heat. The whole thing hinges on temperature control at the custard stage.

• Never let it boilCook in a bowl set over barely simmering water, stirring constantly, until the mixture coats a spoon, around 170-175F. Much past 180F the yolks begin to scramble and the sauce turns grainy; straining may rescue it but the texture will suffer.
• Powdered sugarIn books of this period the term usually meant sugar ground fine, which the modern confectioners' or icing sugar will stand in for. Modern icing sugar contains a little cornstarch, but the amount is small enough that granulated sugar can be substituted without much difference.
• Add the brandy slowlyThe instruction to add it "very slowly" is not decorative. Spirit poured into creamed butter all at once splits the emulsion; drop by drop with steady beating keeps it smooth.
• Egg whitesThe beaten whites are folded into hot custard but are never themselves brought to a safe temperature. Use pasteurized whites, or pasteurized eggs throughout, if serving anyone elderly, pregnant, very young or immune-compromised.
• Order of workBeat the whites to soft peaks while the custard cooks, and pour the hot custard onto them in a thin stream while whisking. Waiting means either deflated whites or a custard that has begun to set.
• Milk or creamWhole milk gives a lighter, more pourable sauce; heavy cream gives one rich enough to stand on the plate. Either works, but do not use skim, which offers no fat to buffer the yolks.
• Yield and servingA generous pint or more once the whites are folded in, enough for six to eight servings alongside plum pudding, steamed fig pudding or a baked apple pudding. Serve warm and freshly made; a foam sauce of this kind will separate on standing.