Makes about 2 1⁄2 pounds
Melt butter in a heavy saucepan. Add brown sugar and salt and stir until thoroughly combined. Stir in corn syrup and mix well. Gradually add milk, stirring constantly.
Cook and stir over medium heat until candy reaches firm ball stage, or 245 degrees F on candy thermometer. It will take about 12 to 15 min.
Remove from heat, stir in vanilla or maple. Pour into a buttered 9 inch square pan, then cool and cut into squares.