In a small mixing bowl, combine the garlic, sherry vinegar, Dijon, and sea salt with a fork. Whisking vigorously with the fork, drizzle in olive oil and then whisk in sour cream. When mixture is thick and creamy, slowly whisk in buttermilk. Finally, add the crumbled Parmesan, and whisk vigorously to combine.
Chill dressing in the fridge while you prepare the salad.
For the Napa cabbage wedge salad:
Keeping the core intact, slice Napa cabbage lengthwise into four equal quarters. Arrange on a large platter.
Either with a mandoline or a sharp knife, carefully cut the red onion into paper thin slices. Core and cut apples into 1/8-inch thick slices. In a medium-sized bowl, toss apples and onions with a pinch of sea salt and a tablespoon of the prepared dressing.
Tuck dressed onion and apple slices all around and between the leaves of the cabbage wedges. Drizzle the Napa wedges with most of the remaining dressing. Finish with chives, a pinch of sea salt, plenty of fresh ground black pepper, and scattered Parmesan.