Preheat your oven to 375 degrees Fahrenheit.
While the oven is heating, take the package of King’s Hawaiian rolls and carefully cut them in half lengthwise. Next, spread the butter on the bottom halves of the rolls.
Place them in the oven-safe baking tray (or any baking dish) and bake for about 7 minutes, or until they are golden brown and toasty.
In a saucepan, bring 2 cups of water to a light boil. Once boiling, whisk in the gravy mix until it’s smooth and combined. Bring it to a light boil.
Place the deli roast beef in the au jus for about 1 minute. Remember, don’t leave it in too long, or you risk toughening the meat. After a minute, carefully remove the beef and set it aside.
Once the rolls come out of the oven, layer them with 6 slices of sharp cheddar cheese. Next, top the cheese with the warm roast beef, followed by 3 oz of crispy fried onions for that irresistible crunch. Finally, add a layer of 6 slices of mozzarella cheese on top.
In a small bowl, mix together 2 tablespoons of melted butter with 1 teaspoon each of garlic powder and onion powder. Brush the mixture over the top of the rolls.
Bake for an additional 5 to 7 minutes or until the cheese is melted, and the buns are toasty golden brown.
Once out of the oven, slice the sliders into individual portions. Serve them with the extra au jus for dipping and with a side of creamy horseradish sauce for a zesty kick.