• In a large skillet over medium heat, melt the butter. Using a mandolin (or a knife), thinly slice the onions. Add the onions and saute for 12-15 minutes, until onions are soft and browned.
• Add the parsley, salt, and pepper, stir to combine, take off the heat, and set aside.
• Preheat the oven to 350°F.
• Butter a 9x13 pan.
• Take the rolls out of the package, leaving the rolls intact.
• Next, take a large knife and slice the rolls across, so you have the tops and bottom separated.
• Place the bottom, cut side up, into a 9x13 baking dish.
• Top with half of the cheese slices.
• Add the roast beef.
• Top evenly with the sauted onions.
• Add the remaining cheese, then add the tops of the rolls over the onions.

Make the butter mixture:

• In a small bowl, stir together the melted butter and onion soup mix.
• Drizzle the butter sauce over the top of the sliders (or you can brush it on).
• Cover loosely with foil, and bake for 25 minutes.
• Take the foil off and bake an additional 5 minutes to brown the rolls.
• While the rolls are baking, prepare the au jus, per the package directions, with the water.
• Serve the rolls with an optional garnish of parsley and au jus on the side for dipping.