In a heavy 2-quart saucepan combine sugar, light corn syrup, and water.
Cook over medium-high heat to boiling, stirring constantly with a wooden spoon to dissolve sugar. This should take 5 to 7 minutes.
Avoid splashing mixture on sides of pan.
Carefully clip candy thermometer to side of pan.
Cook over medium heat, without stirring, till thermometer register 260 degrees, hard-ball stage. Mixture should boil at a moderate, steady rate over the entire surface.
Reaching hard-ball stage should take about 15 minutes.
Remove saucepan from heat; remove thermometer from saucepan. I
n a large mixer bowl, immediately beat egg whites with a sturdy, freestanding electric mixer on medium speed till stiff peaks form.
Gradually pour hot mixture in a thin stream over egg whites, beating with the electric mixer on high speed and scraping the sides of the bowl occasionally.
This should take about 3 minutes.
Add vanilla. Continue beating on high speed. When beaters are lifted, mixture should fall in a ribbon, but mound on itself and not disappear into remaining mixture.
Fold in chopped walnuts.
Drop a spoonful of the mixture onto waxed paper.