Combine the brown sugar, corn syrup, vinegar, and salt in a heavy 3-quart saucepan.
Set over low heat and stir until sugar is dissolved.
Increase heat and bring to boiling, stirring constantly.
Add evaporated milk slowly, stirring constantly, so that boiling does not stop.
Set candy thermometer in place.
Cook, stirring constantly, until mixture reaches 248°F (firm-ball stage).
During cooking, wash down crystals from sides of pan with a pastry brush dipped in water.
Remove from heat and remove thermometer.
Immediately pour mixture into a buttered shallow pan or platter; do not scrape saucepan.
When mixture is just cool enough to handle, pull a small portion at a time with buttered hands.
Work in a cool place.
Pull until candy is ivory colored and no longer sticky to the touch.
Twist pulled strip slightly and place on waxed paper or a board.
Cut with scissors or sharp knife into 1-inch pieces.
For storing, wrap pieces in moisture-vapor-proof material and store in a tightly covered container in a cool, dry place