2/3 cup cocoa
2 cups granulated sugar
1 cup light corn syrup
1/8 teaspoon salt
1 cup evaporated milk
1/2 cup water
1/4 cup butter
1 teaspoon pure vanilla extract

Combine cocoa, sugar, corn syrup and salt in a heavy 3-quart saucepan. Add evaporated milk and water; bring to a boil over medium heat, stirring constantly. Cook, stirring frequently, until mixture forms a firm ball in cold water, or registers 245 degrees F on a candy thermometer.

Remove from heat; drop in butter and vanilla extract, stirring to completely blend in butter. Pour into buttered 9-inch square pan; let cool.

Cut into squares, and wrap in wax paper.