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Butterscotch Sauce
1/2 cup Karo, Blue Label 1/2 cup Karo, Red Label 1/2 cup granulated sugar 1 tablespoon top milk 1 tablespoon butter Few grains salt 1/2 teaspoon vanilla Combine all the ingredients except the vanilla, and boil until it forms a short thread, 238 degrees F., then add two tablespoons boiling water and the vanilla. Use hot or cold.
A simple boiled sugar sauce that hinges entirely on hitting one temperature. The only real obstacles are two discontinued Karo labels and one dairy term nobody uses any more.
- Karo Blue and Red LabelBlue Label was the plain, near-colorless corn syrup; Red Label had refiners' syrup blended in, giving darker color and a fuller molasses-edged flavor. Substitute 1/2 cup light corn syrup and 1/2 cup dark corn syrup.
- Top milkThe cream that rose to the top of a bottle of unhomogenized milk — richer than milk, thinner than heavy cream. A tablespoon of half-and-half or light cream is the equivalent.
- Hit 238°F and stopHit 238≥F and stop -- This is the whole recipe. Use a candy thermometer rather than the "short thread" test; below 238°F the sauce stays thin and syrupy, and the further above it you go the thicker and stickier it sets when cold. Pull the pan off the heat the moment it reads.
- The finishing waterThe two tablespoons of boiling water thin the cooked syrup back to sauce consistency. Use boiling water as directed: cold water dropped into sugar at 238°F will spit violently. Add it off the heat, at arm's length.
- Pan choiceUse a heavy saucepan at least three times the volume of the ingredients. A cup and a half of syrup climbs alarmingly as it boils, and thin pans scorch the sugar against the bottom before the mass reaches temperature.
- Don't stir once it boilsStir only until the sugar dissolves. Agitation afterward encourages crystals, though the corn syrup here is doing most of the work of preventing that.
- Vanilla goes in lastAdded at 238°F it would largely cook off. Stirring it in after the water preserves the aroma.
- Yield and keepingAbout a cup and a quarter — enough for six to eight servings over ice cream or steamed pudding. It thickens when cold; keep it covered in the refrigerator and use within a week or so, warming gently and adding a teaspoon of water if it has gone stiff.
Butterscotch sauce belongs to the era when American corn syrup manufacturers were teaching home cooks to use their product, and this recipe reads like exactly that: two Karo labels named by color, in equal measure, as though the reader would have both on the shelf. Corn Products Refining Company sold Karo in Blue, Red and Green labels from the early twentieth century, and promotional booklets and branded recipe pages of the period pushed the syrups hard into candy-making, where corn syrup's real virtue is chemical — it interferes with sucrose crystallizing, so a boiled sauce stays smooth instead of turning grainy. The name butterscotch is older than the sauce and its origin is disputed; it is often traced to Doncaster in Yorkshire, where a boiled butter-and-sugar sweet was sold in the nineteenth century, with "scotch" generally explained as scoring or cutting the cooled slab rather than any Scottish connection. What the labels tell you is that this page was written for a cook who bought syrup by brand, kept a thermometer, and thought 238°F a perfectly ordinary instruction.