Rinse grapes and pat to dry. In a large bowl, mix softened cream cheese, sour cream, white sugar, and vanilla. You can use a mixer or mix by hand with a spatula. Add the grapes to the cream cheese mixture and stir thoroughly to coat. Transfer to a serving bowl.
Sprinkle brown sugar over the grape mixture. Cover and refrigerate until ready to serve. Right before serving sprinkle nuts on top.
Tip: For a healthier version you can substitute Greek yogurt for the sour cream.