Let the grapes drain on paper towels while you prepare the salad dressing.
If you have walnut halves, chop them into pieces.
Toast walnuts by heating up a skillet to medium to medium-high heat. Add walnuts to the skillet. Let walnuts toast by simply heating them in the skillet, you may stir them once or twice.
When nuts become fragrant and brown, remove them immediately from the skillet and place them on a plate. By placing the nuts on a cool plate, you will stop the cooking process.
Make the salad dressing by combining the sour cream, cream cheese, lemon juice, and powdered sugar in a medium-sized bowl. Beat until well blended.
Add vanilla extract to the dressing and mix it in.
Add walnuts and grapes to the bowl with the dressing.
Fold in grapes and walnuts until they are incorporated fully into the dressing.
Place the grape salad in a covered bowl.
Refrigerate the salad for about 1 hour before serving.