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POTATO CAKE, SWEET (another way)
Take a quarter of a pound of boiled potatoes, dry and floury, and beat them to flour. Mix with this one ounce of ground rice, an ounce of sweet almonds and four bitter ones blanched and pounded together, and three ounces of sugar rubbed upon a fresh lemon for a few minutes to extract the flavour and then crushed to powder. Mix these dry ingredients thoroughly, and stir into them the well-beaten yolks of five eggs. Beat the mixture for five or six minutes, and add the whites of the eggs beaten to a firm froth. Turn the paste into a well-buttered tin, and bake in a brisk oven for about forty minutes. Probable cost, 9d. Sufficient for a small cake.
This is a light almond-and-potato sponge of a kind common in Victorian pastry work, but it is built on an ingredient that is no longer sold or used as food.
- Bitter almonds are the problemBitter almonds contain amygdalin, which releases hydrogen cyanide when the nut is crushed and moistened, which is what happens when they are blanched and pounded with the sweet almonds here. Four nuts in a small cake is the flavouring quantity typical of the period rather than a large dose, but the cyanogenic content of individual nuts varies and there is no way to measure it in a domestic kitchen.
- They are not on sale for a reasonUnprocessed bitter almonds cannot legally be sold as food in the United States and are restricted in the UK and EU. Commercial bitter almond flavouring is a processed extract from which the cyanogenic compounds have been removed; it is not the same material and is not a like-for-like substitute in a recipe that uses the whole nut as bulk.
- Baking does not make it safeHeat drives off some hydrogen cyanide, but the amount remaining after forty minutes in a covered mass of batter is not predictable. There is no home method for testing it, so there is no way to judge the result.
- What the bitter almonds were doingThey supplied the marzipan note that sweet almonds alone cannot give — the same job now done by a few drops of almond extract. If you want a cake of this type, work from a current recipe rather than trying to patch this one.
- Other period details, for reading"Beat them to flour" means working the cooled floury potatoes to a powder, in practice by sieving or ricing; a brisk oven is usually taken to be somewhere in the 400-450F range, though the recipe gives no temperature. The price of 9d is a Victorian cost note, not a measurement.
Potato in a sweet cake looks eccentric now but was unremarkable in nineteenth-century baking: cooked floury potato, sieved fine, gives moisture and a tender crumb at a fraction of the cost of ground almonds, and it appears in cakes and puddings in British and continental cookbooks of the period. The book gives several potato cake variants side by side, and the "another way" heading here reflects that; economy in the use of an expensive ingredient is a plausible reason, though the text does not say so. The bitter almonds are equally of their time: they were long an ordinary grocer's item, sold alongside sweet almonds and used in tiny numbers for flavour, with the poisoning risk understood in a rough way well before it was regulated. Rubbing sugar against a lemon rind to take up the oil, as the recipe directs, is the older technique that zesting and lemon extract later replaced.