In a large mixer bowl, sprinkle gelatin over ⅓ cup cold water and let stand until softened, 5 min.
In a small, heavy saucepan, combine sugar and ¼ cup water. Stir over medium-high heat until sugar dissolves; remove spoon. Brush insides of pan with a wet pastry brush to remove any sugar crystals and place a candy thermometer into mixture. Boil (do not stir) until syrup until syrup registers 235°F (soft-ball stage), about 10 min. Pour into gelatin.
With the whisk attachment, beat mixture on high until soft peaks form, about 7 min. Add vanilla and use immediately.