Bring 4 quarts of salted water to a boil and drop in the shrimp. Wait 1 minute; empty the pot into a colander set in the sink. Let the shrimp cool in the colander.
Transfer the cooled shrimp to a bowl.
In a separate small bowl, whisk the sour cream and mayonnaise together well.
Pour the dressing over the shrimp and toss gently. Add the grape