01 - In a large mixing bowl, toss together the drained pineapple chunks, halved grapes, mandarin orange segments, mini marshmallows, and chopped nuts if using.
02 - In a separate medium bowl, whisk together the sour cream, mayonnaise, honey or sugar, and vanilla extract until completely smooth and well blended.
03 - Pour the dressing over the fruit mixture and gently fold until every piece is evenly coated, taking care not to crush the soft fruit.
04 - Cover the bowl with plastic wrap and refrigerate for at least 1 hour to allow the flavors to meld and the dressing to set.
05 - Give the salad one last gentle toss to redistribute the dressing, then transfer to a serving bowl and serve chilled.