In a large bowl, toss the diced apples with the lemon juice and sugar. Mix in the celery, grapes, and nuts.
In a separate bowl, whip the heavy cream until it forms peaks. Fold in the mayonnaise gently. Combine this mixture with the apple mix and season with kosher salt. Taste and adjust seasoning as needed.
Chill the salad for at least 1 hour or overnight for the best flavor. Serve alone or on a lettuce leaf.