Preparation

• Preheat the oven to 350°F (175°C). Spread 2 tablespoon butter all over 9x13-inch baking pan. Line pan with parchment paper.
• Using a serrated bread knife, carefully slice the entire block of Hawaiian rolls in half horizontally, keeping the individual rolls attached (see note 1). Place the bottom half of the rolls in the prepared pan.
• Layer with 6 slices of cheese, roast beef, optional french-fried onions, remaining 6 cheese slices, and top slab of rolls.
• In a small, microwave-safe bowl, melt butter. Add 1 tablespoon of au jus mix plus remaining butter ingredients. Whisk until well combined. Spread mixture evenly over tops of rolls and sides (use about ¾). Refrigerate any leftovers for later use on steak or bread.
• Bake the sliders uncovered until the cheese is gooey and tops of rolls are golden brown, about 15–20 minutes.
• For au jus, heat remaining packet in a small saucepan over medium heat. Add cold water (whatever is indicated on package) and whisk. Bring to a boil, then simmer until slightly thickened.
• Remove and cut sliders into squares, along the roll divisions, with a very sharp knife. Serve au jus with the sliders.