2 c. (1/2 L) firmly packed dark brown sugar
1/4 c. (60 g) butter
1 tbsp. vinegar
Pinch of salt

Oil a jelly-roll pan or an 8 x 8 inch pan. Combine all the ingredients with 2 tablespoons boiling water in a 3-quart heavy pot, stirring to blend well. Place over moderate heat, stirring as the sugar dissolves and the mixture comes to a boil. Cover and let boil for 2 to 3 minutes, then uncover and wash down the sides of the pot with a pastry brush dipped in cold water.

Boil slowly over moderate heat until it reaches the hard-crack stage (290 degrees), stirring gently, without touching the sides of the pot, only if it starts to scorch. Pour it out into the oiled pan and let cool partially, then cut into squares. When completely cool and hard, cut or break into pieces and transfer to an airtight tin. 1 pound.