Meanwhile, in 1-quart saucepan, place 1/2 cup of the milk. Sprinkle gelatin over milk; let stand 5 minutes to soften. Stir in remaining 1/2 cup milk and 1/4 cup SPLENDA. Cook on low heat, stirring frequently, until gelatin is completely dissolved (do not boil). Pour milk mixture into blender. Add ricotta cheese and vanilla; cover and blend until pureed. Pour into large bowl; stir in whipped topping and yogurt.