In a blender or small food processor blend together garlic, mustard, lemon juice, vinegar, salt and pepper to taste.
With the motor running add the oil in a slow stream and blend until mixture is combined.
Add the sour cream, 3/4 cup blue cheese, and water, or enough to obtain desired consistency. Blend dressing until it is combined well; transfer to a bowl. Stir in the additional blue cheese.
Servings: about 1 1/3 cups