Butter Rum Caramels

1 1/2 cups heavy cream
1 cup sugar
1 cup light brown sugar
1/3 cup light corn syrup
1/2 stick unsalted butter
1/2 teaspoon salt
2 teaspoons rum or rum extract

Butter an 8 inch square metal baking pan ( do not use glass) and set on a rack. In a 5 qt. heavy kettle cook cream, sugars, corn syrup, butter, and salt over moderate heat. Stir constantly with a wooden spoon & wash down any sugar crystals forming to the side of the pan, with a brush dipped in cold water, until sugars are completely dissolved, about 15 minutes. Boil mixture without stirring, until a candy thermometer registers 245�F, about 15 minutes.