In a large skillet over medium heat, melt 3 tablespoons of unsalted butter. Add the sliced onions and coat them in the butter. Cook, stirring occasionally, for about 12-15 minutes until the onions are soft and browned but not burnt.

Add 2 teaspoons of minced thyme, 1/4 teaspoon kosher salt, and 1/4 teaspoon black pepper, stir to combine, then take off the heat and set aside.

Preheat the oven to 350°F. Take the sweet rolls out of the package, leaving them intact, and use a large knife to slice the rolls across, separating the tops and bottoms.

Place the bottom halves, cut side up, into an 11x7 baking dish. Top with half of the provolone cheese. Add the sliced roast beef and spread the cooked onions over the beef. Add the remaining provolone cheese, then place the tops of the rolls on top.

In a small bowl, stir together the melted butter and 1 1/2 tablespoons of onion soup mix. Brush this mixture evenly over the tops of the rolls.

Cover the dish loosely with foil, ensuring the foil doesn’t touch the tops of the rolls, and bake for 25 minutes.

Remove the foil and bake for an additional 5 minutes to brown the tops of the rolls.

While the rolls are baking, prepare the au jus according to the package directions using 3 cups of water.

Serve the warm sliders with an optional garnish of parsley and au jus on the side for dipping.