Prepare a quarter-sheet pan, 12 × 8 inches (30 × 20 cm), or other suitable pan of approximately the same size, by lining the bottom with baking paper and dusting lightly with cornstarch.
Sprinkle the gelatin over the first measurement of water (be sure to pour the water in a wide enough bowl so that all of the gelatin will be moist) and set aside to soften.