Preheat oven to broil. Slice the Hawaiian rolls horizontally and place them cut side up on a lined baking sheet. Melt 4 tablespoons of butter and brush the inside of the rolls. Broil for 3-4 minutes until golden brown.

Reduce oven temperature to 350°F. In a large bowl, mix the ground beef with salt and pepper. Press the mixture evenly into a 9x13 casserole dish and bake for 20 minutes.

While the beef is baking, sauté the diced onions in a pan over low heat with 1 tablespoon of butter for about 15 minutes until browned and soft.

Once the beef is cooked, carefully drain off all excess fat and liquid from the pan to prevent the rolls from becoming soggy.

To assemble, place a layer of pickles on the bottom toasted buns. Use spatulas to transfer the cooked beef slab onto the buns. Layer with cheese and the sautéed onions, then replace the top buns.

Brush the top of the rolls with the remaining 1 tablespoon of melted butter. Return to the oven and bake for 15 minutes or until the cheese is fully melted.

In a small bowl, whisk together the mayonnaise, ketchup, mustard, pickle juice, and cayenne pepper to create the dipping sauce.