In small bowl, sprinkle gelatin over 1/4 cup water; let stand to soften. In 2-quart saucepan, mix 1/3 cup sugar, the salt, sour cream, milk and egg yolks. Cook over medium heat 10 to 15 minutes, stirring constantly, until very hot; do not boil. Stir in softened gelatin. Cover surface with plastic wrap; refrigerate until slightly thickened, 45 to 60 minutes.