Directions

1. Spray an 11 3/4-by-16 1/2-inch baking pan (this is a half-sheet pan) with vegetable-oil spray. Set aside in a spot where it will not be moved. In a 2-quart saucepan, combine cream and sweetened condensed milk; set aside.
2. In a heavy 6- to 8-quart saucepan, combine corn syrup, 1 cup water, sugar, and salt. Clip on candy thermometer. Over high heat, cook until sugar is dissolved, stirring with a wooden spoon, 8 to 12 minutes. Brush down sides of pan with a pastry brush dipped in water to remove any sugar crystals.
3. Stop stirring, reduce heat to medium, and bring to a boil. Cook, without stirring, until temperature reaches 250 degrees (hard-ball stage), 45 to 60 minutes. Meanwhile, cook cream mixture over low heat until it is just warm. Do not boil. When sugar reaches 250 degrees. slowly stir in butter and warmed cream mixture, keeping mixture boiling at all times. Stirring constantly, cook over medium heat until thermometer reaches 244 degrees (firm-ball stage), 55 to 75 minutes. Stir in vanilla. Immediately pour into prepared pan without scraping pot. Let stand uncovered at room temperature for 24 hours without moving.
4. To cut, spray a large cutting board generously with vegetable-oil spray. Unmold caramel from pan onto sprayed surface. Cut into 1-by-1 1/4-inch pieces, or other shapes. Wrap each in cellophane or waxed paper.