In a saucepan, combine sugar and water over medium heat until sugar dissolves.
Mix cornstarch with 1/2 cup of water until smooth.
Gradually add cornstarch mixture to the saucepan, stirring constantly.
Add lemon juice and bring to a boil.
Reduce heat and simmer for about 10 minutes, stirring frequently.
Stir in rosewater and food coloring, if desired.
Add chopped nuts and mix well.
Pour the mixture into a greased baking dish and spread evenly.
Allow to cool for at least 4 hours before cutting into squares.
Dust with powdered sugar before serving.