Butter 2 large baking sheets; set aside.

Butter sides of a heavy 3-quart saucepan. In pan combine sugar, corn syrup, water, and butter. Cook and stir over medium-high heat until mixture boils. Clip a candy thermometer to side of pan. Reduce heat to medium-low; continue boiling at a moderate, steady rate, stirring occasionally, until the thermometer registers 275F, soft-crack stage (about 30 minutes). Stir in nuts; continue cooking over medium-low heat, stirring frequently, until thermometer registers 295F, hard crack stage (15 to 20 minutes more).

Remove pan from heat; remove thermometer.

Quickly sprinkle baking soda over mixture, stirring constantly. Immediately pour onto prepared baking sheets. Use 2 forks to lift and pull candy as it cools. Cool completely; break into pieces. Store tightly covered up to 1 month.