1. In heavy 3-quart saucepan over medium heat, heat sugar, corn syrup, salt, and 1/2 cup water to boiling, stirring constantly until sugar dissolves.

2. Set candy thermometer in place and continue cooking, stirring frequently, until temperature reaches 300 degrees F. or hard-crack stage (when small amount of mixture dropped into very cold water separates into hard and brittle threads), about 30 minutes.

3. Remove saucepan from heat; stir in margarine or butter, vanilla extract, baking soda, and nuts. Immediately pour onto ungreased large cookie sheet. With 2 forks, quickly lift and stretch nut mixture into about 14" by 12" rectangle.

4. Cool brittle completely on cookie sheet on wire rack. With hands, break brittle into small pieces. Store in tightly covered container.