1. Blend the frozen strawberries in the blender until just starting to break apart.
2. Place the sugar substitute and the vanilla into the blender.
3. Blend until starting to mix together.
4. Add the sour cream and blend.
5. Mixture should be just about smooth but be sure to leave a few small pieces of strawberries.
6. Mix in the yogurt just until it is blended with the other ingredients.
7. Serve immediately garnished with the whip topping and a whole strawberry.