Bitter Sweet Frosting

A two-layer icing: a plain white sugar frosting spread on the cake, then a thin veil of melted unsweetened chocolate poured over it. The contrast of sweet base and bitter top is the whole point, so keep the two layers distinct rather than stirring the chocolate in.

• Bitter chocolateOne square means one ounce of unsweetened baking chocolate, the standard wrapped square of the period. Modern squares are still an ounce, but many bars are scored at half an ounce, so weigh rather than count.
• The liquid is the variableTwo cups of powdered sugar with eight tablespoons of milk gives a pourable glaze, not a spreadable frosting. Add the milk a spoonful at a time and stop when it holds a soft ridge; you will likely want three to four tablespoons.
• ShorteningHere 'shortening' most likely means vegetable shortening, which gives a very white, slightly waxy frosting; in period usage the word could also cover other solid fats. Softened butter substitutes one for one and tastes better, though it sets firmer in the refrigerator.
• Sift the sugarPowdered sugar packs and lumps in the box. Sift it before mixing or the frosting will be gritty, and the thin chocolate top will show every bump beneath it.
• The chocolate layerMelt the square gently over hot water or in short bursts in the microwave, to about 110F. Overheated unsweetened chocolate scorches and turns dull and grainy, and there is no sugar or cream here to rescue it.
• Order of workLet the white layer set for ten to fifteen minutes before pouring the chocolate, or the two will marble together. Spread the chocolate quickly with an offset spatula while it is still fluid; it firms up fast on a cool cake.
• YieldEnough to cover the top and sides of an 8- or 9-inch layer cake, or the top of a 9x13 sheet. Double it for a generous filled two-layer cake.