Cocoa Icing
6 tablespoons hot water 6 tablespoons cocoa 3/4 cup granulated sugar 1/2 teaspoon salt Mix sugar and water until smooth; add cocoa and salt, and stir until creamy. Spread between layers and on top and sides of cake.
A four-ingredient uncooked frosting that depends entirely on getting the sugar into solution. Everything below follows from that.
- Dissolve the sugar firstThe hinge is the order of operations: granulated sugar must go into the hot water and be stirred until no grit can be felt on the tongue before the cocoa goes in. Cocoa added early thickens the mixture and traps undissolved crystals, and the icing sets sandy.
- Use water that is genuinely hotThe recipe specifies no temperature, but heat gets the sugar into solution far faster. Six tablespoons will hold three-quarters of a cup of sugar even cold, but only with long stirring. If it refuses to clear, warm the bowl over a pan of simmering water rather than adding more liquid.
- Which cocoaThe quantity implies unsweetened cocoa powder, and an American kitchen of the period would most likely have had natural cocoa, though Dutch-process was also on sale. Dutch cocoa works and gives a darker, milder result; natural cocoa is more acidic and tastes sharper against this much sugar.
- Consistency and timingThis sets as it cools, so spread it while still fluid and work quickly. If it stiffens on the way to the cake, a teaspoon of hot water stirred in will loosen it.
- SaltHalf a teaspoon is a great deal for this quantity and may well taste salty; nothing in the text settles whether it is intended or an error. Use fine salt so it dissolves with the sugar.
- YieldRoughly a scant cup, enough for a modest two-layer 8-inch cake if spread thinly. For a generous coating on a 9-inch layer cake, make one and a half times the quantity.
- KeepingWith no fat and no egg, this dries to a thin firm shell within a few hours and will crack when the cake is cut the next day. It is at its best the day it is made.
The New Royal Cook Book was published by the Royal Baking Powder Company, one of the great promotional cookbooks of the early twentieth century, given away or sold for pennies to put the brand in domestic circulation. Its cake chapter is where that purpose shows most plainly, and icings like this one are the plain-cook companions to it: no butter, no egg white, no candy thermometer, nothing to fail. Cocoa powder had by then become an everyday grocery rather than a luxury, following the nineteenth-century development of presses that removed most of the fat from chocolate liquor and left a cheap, shelf-stable powder; American manufacturers were selling it by the tin to households well before the First World War. What the recipe records is a moment when chocolate flavour in a home kitchen could arrive as cocoa and sugar stirred with hot water rather than as melted bar chocolate.