Caramel Frosting II

A three-ingredient cooked frosting of the fudge family, closer to maple butter candy than to a modern buttercream. The whole thing turns on how far the syrup cooks, not on the clock.

• Ignore the thirteen minutesBoiling time depends on your pan, your burner and the water in your cream. Cook to the soft-ball stage, 236-240F on a candy thermometer; at that point the mixture will hold a soft shape when a drop is chilled in cold water. Thirteen minutes on a modern high-output burner in a thin pan can overshoot into hard-ball territory and give you an unspreadable slab.
• Grated maple sugarMaple sugar was commonly sold as a hard pressed cake, which is why the instruction is to grate it. Granulated maple sugar is the closest modern equivalent; firmly packed light brown sugar plus a teaspoon of maple syrup is a workable stand-in, though the flavor is flatter.
• Cream"Cream" here means something richer than milk, though period cream was not standardised and was often thinner than today's heavy cream. Half-and-half or milk will scorch more readily and produce a thinner frosting.
• Pan and stirringUse a heavy saucepan at least three times the volume of the ingredients: butter and cream foam up hard. Stir until the sugar dissolves, then leave it mostly alone, wiping the sides down with a wet brush to keep crystals from seeding the batch.
• Beating and the working windowCool the syrup off the heat for a few minutes, then beat until it loses its gloss and thickens. It sets fast once it turns; spread while still warm and pourable, and if it stiffens too far, set the pan over low heat or add a spoonful of hot cream to loosen it.
• YieldAbout a cup, enough to cover the top and sides of a single 8-inch layer, or to fill and top a thin two-layer cake sparingly. It is very rich; a thin coat is the intent.