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Potato Biscuits
Bake half a dozen large potatoes, and when they are done enough, burst them open, and scoop out the inside with a tea-spoon until there is a quarter of a pound of the flour. Pass this through a fine sieve, and mix with it the well-beaten yolks of eight eggs, the grated peel of half a lemon, and half a pound of pounded and sifted sugar. Beat the paste until it is quite light, then add the whites of the eggs beaten to a firm froth. Make some small paper cases, oil them, and half fill them with the batter. Strew a little sugar over them, and bake in a moderate oven. If liked, a little bright-coloured jelly may be put over the biscuits before serving. Time to bake, about twenty minutes. Probable cost, 1s. 2d.
A flourless sponge biscuit in which dry baked potato does the work of wheat flour. It behaves like a genoise batter, so the handling of the eggs matters more than anything else.
- "A quarter of a pound of the flour"This means the dry, floury interior of the baked potatoes, not wheat flour — there is none in the recipe. Four ounces of scooped potato is roughly three-quarters of a cup, lightly packed, and six large baking potatoes will give you far more than that, so use the best of the crumb and keep the rest for something else.
- Bake, do not boilThe potatoes are baked because the point is to drive off water. A boiled or steamed potato carries too much moisture and the batter will be slack and gluey. Sieve the flesh while it is still hot; cold potato turns pasty as it is pressed through.
- Moderate oven350F/175C. Twenty minutes is about right for small cases; the biscuits should be set and lightly coloured, with a dry crumb at the centre.
- The hinge: fold, don't beatAll the lift comes from eight eggs and nothing else. Beat the yolk-potato-sugar paste hard and long to aerate it, then fold the firm whites in with a spatula in three additions. Stirring them in collapses the only leavening in the recipe.
- Paper casesCases of this period were generally made at home from stiff paper folded around a small mould. Paper petit-four cases or a mini muffin tin lined with parchment cups does the same job; brush the inside with a neutral oil as directed, since there is no added fat in the batter to prevent sticking.
- Sugar"Pounded and sifted sugar" is what we call caster sugar. Half a pound to four ounces of potato is a sweet mixture by modern taste, but reducing it will also reduce the volume the yolks can hold, so cut it by no more than a quarter.
- YieldExpect about 20 to 24 small biscuits from half-filled cases. With no added fat beyond the yolks they stale quickly, and are best on the day they are baked.
- The jelly finishThe recipe leaves the jelly unspecified beyond "bright-coloured"; a redcurrant or apple jelly, warmed slightly to spread, suits. Add it once the biscuits are cool, or it runs off.
This reads as an exercise in what a starch other than wheat will do: potato supplies the body, eggs supply the structure and the rise, and nothing else is needed. Flourless potato sponges of this type belong to a broad European confectionery tradition — potato starch and sieved cooked potato both turn up in German and Austrian torte recipes of the nineteenth century, and potato flour was sold in Britain as an alternative to arrowroot. The costing of 1s. 2d. is a reminder that Cassell's expected its readers to weigh a dish's expense as carefully as its method.