Preheat oven to 450ºF.
In a mixing bowl, combine beef and pork with Kosher salt, spices, egg, breadcrumbs and parsley. Roll and arrange 2-inch meatballs on baking sheet and spray with cooking spray. Bake to lightly brown 10-12 minutes then remove.
Bring a medium pot of water to boil, salt water and cook barley to tender, 20 minutes, drain.
Meanwhile, melt butter over medium heat. Add onions, season with salt and pepper, and cook to golden in color and sweet, 15-20 minutes, stirring frequently.
In a casserole, combine barley, onions and sauerkraut. Top with Swiss cheese and arrange meatballs in casserole. Cool and cover for make-ahead meal.
Combine sour cream with ketchup, relish, salt and pepper, and store in a plastic food storage bag.