Toast the pecans in a skillet on medium-low heat until fragrant and slightly browned. Pour onto a plate and let cool.
Beat the cream cheese, granulated sugar, and vanilla with a mixer on medium speed. Stir in the sour cream.
Wash the grapes and dry them. If they are large or you prefer smaller bites, cut them in half--otherwise, leave them whole. Stir them into the cream cheese mixture.
Place the grape mixture into a 9 x 13-inch serving dish. Sprinkle brown sugar and pecans on top. Store in the refrigerator.
Notes
Brown Sugar
The original recipe calls for 1/2 cup of brown sugar sprinkled on top. I reduced the amount, so this salad has less sugar. Add the omitted 1/4 cup if you prefer a sweeter dish.
Substitution
You can substitute 8 ounces of mascarpone for the cream cheese.