Mix sugar, syrup, and water in a 2 quart glass measure.
Microwave uncovered on high, stirring twice, 15- 17 minutes until sypur reaches hard ball stage (260 on instant- read thermometer or forms a hard ball when a small amount is dropped into very cold water).
Meanwhile, beat egg whites in med-size bowl with an electric mixer until soft peaks form when beaters are lifted.
Gradually add gelatin, beating until whites are stiff and glossy.
While beating, constantly pour the hot syrup into the egg-white mixture and continue beating until mixture is very thick.
Stir in walnuts and vanilla.
Spread into prepared dish.
Let stand at room temperature until completely cool and set, about 4 hours or overnight.