In a 3-quarte saucepan mix sugar, 1 cup water, and 1 cup corn syrup. Cook over medium heat about 25 minutes, stirring occasionally, until 240°F (116°C) on a candy thermometer.
Stir in butter and cashews.
Cook another 10-15 minutes, stirring constantly, until candy thermometer registers 300°F (149°C). Stir constantly so that it doesn't burn.
Remove from heat and immediately stir in Baking Soda Mixture until light and foamy.
Pour half of the candy onto each prepared baking sheet and spread to about ¼-inch thick with buttered spatula(s).
Cool completely, at least one hour.
Break into pieces.