In heavy 3-quart saucepan combine sugar, corn syrup, and 1/2 cup water.
Cook and stir till sugar dissolves.
Bring syrup to boiling; blend in butter or margarine.
Stir frequently after mixture reaches the thread stage and candy thermometer registers 230° Add cashews when temperature reaches soft-crack stage, 280°.
Stir constantly till temperature reaches hard-crack stage, 300°.
Remove from heat.
Quickly stir in soda, mixing well.
Pour onto two buttered baking sheets or two buttered 15 1/2x10 1/2x 1-inch baking pans.
As the candy cools, stretch it by lifting and pulling with two forks from edges to make it thinner.
Loosen candy from pans as soon as possible.
Turn candy over; break in pieces.