Plum Pudding Sauce

A fortified sweet sauce for Christmas pudding, built on the Victorian standby of "melted butter." The one thing to know before starting is that the phrase does not mean what it says.

• "Melted butter" is a flour sauceIn British cookery of this period, melted butter is a thickened butter sauce, not butter liquefied in a pan. The recipe gives no thickening or liquid; a sauce of this kind would typically take four ounces of butter with roughly a tablespoon of flour and up to half a pint of water or milk, simmered until smooth and coating. Plain melted butter is likely to split when the spirits go in.
• The arrowroot alternative"Thick arrowroot" is the lighter, clearer option. The recipe gives no quantities, but about two teaspoons of arrowroot slaked in cold water, stirred into half a pint of hot water or milk and brought just to the boil, answers. Arrowroot thins if held at a boil or reheated hard, so make it at the last minute.
• Ounce and a half of eachMost likely fluid ounces: three tablespoons apiece of sherry, brandy and curaçao, four and a half fluid ounces of spirits in all. Against a half-pint base that is still a strong sauce; start with two-thirds and taste.
• CuraçaoThe orange liqueur of the period, not the blue bar syrup of modern shelves. Cointreau or triple sec is the closest modern stand-in; Grand Marnier works but adds its own brandy note, so pull back the French brandy a little if you use it.
• Add the spirits off the heatStir them in once the sauce is made and the pan is off the burner. Boiling drives off the alcohol and the volatile orange oils, which are the point of the curaçao.
• Sweetening"To the taste" means somewhere around two to three ounces of caster or sifted icing sugar for this quantity, judged against how sweet the pudding itself is. Sugar dissolves best while the base is still hot, before the spirits go in.
• Nutmeg and lemon-peelGrate both fresh and finely; a quarter of a nutmeg and the zest of half a lemon is about right. Dried peel and pre-ground nutmeg give a dusty flavour that the spirits will not cover.
• YieldRoughly three-quarters of a pint of sauce. Serve hot in a warmed sauceboat, as the butter version sets as it cools.