Step 1 Cook the water with the gelatin in a saucepan over low heat until the gelatin dissolves, 3 minutes. Add the sugar and stir constantly until the sugar dissolves, 2 to 3 minutes. Add the vanilla and whipping cream and continue to cook, bringing the mixture almost to a simmer. Do not boil. When hot, add the sour cream and remove the pan from heat. Use a whisk to blend well.
Step 2 Pour the mixture into a 6-cup nonstick mold (or spray a mold with nonstick cooking spray). Refrigerate the dessert until set, about 4 to 5 hours.
Step 3Unmold and serve.