Preheat oven to 450 degrees. Sprinkle kosher salt in a light layer on a baking sheet.
Scrub the potatoes clean and pat dry. Pierce potatoes with a fork all over. Place them on the baking sheet. Bake 1 hour 20 minutes, until easily pierced with a fork.
While potatoes are hot, slice them open and place 1 Tbsp. of butter in each potato. Using a fork, stir 1/4 cup of mozzarella cheese into the flesh of each potato and whip until creamy.
Top each potato with corn, pickles, olives and pickled onions.