Place 2/3 cup water in a small bowl. Sprinkle gelatin on top; let stand until softened, about 15 minutes.
Combine remaining 1 cup water, sugar, and lemon juice in a saucepan over medium heat; bring to a boil, stirring until sugar dissolves. Increase heat and boil syrup, covered, for 3 minutes.
Uncover saucepan and attach a candy thermometer to the side; continue cooking syrup until the temperature reaches 238 degrees F (114 degrees C), about 5 minutes. Remove from heat; stir in gelatin mixture carefully until completely dissolved. Mix in rose water and red food coloring.
Pour syrup into the greased pan. Let stand at room temperature until gelled, about 4 hours. Cover with plastic wrap and chill, 8 hours to overnight.
Cut gelled mixture into 1-inch squares. Dust with cornstarch.
