In a large skillet, melt 4 tablespoons of unsalted butter over medium heat. Add thinly sliced onions and sauté for about 12-15 minutes, stirring occasionally, until they turn soft and golden brown. Incorporate fresh thyme, kosher salt, and black pepper, mixing well to enhance the flavors, then remove from heat and set aside to allow the rich aroma to develop.

Preheat your oven to 350°F (175°C). While the oven heats, take a pack of sweet rolls and slice them in half horizontally while keeping them attached. Arrange the bottom halves in a baking dish, ensuring they fit snugly.

On top of the bottom halves of the sweet rolls, layer half of the provolone cheese, followed by a generous portion of the sliced deli roast beef. Top with the sautéed onions, allowing their sweetness to shine through, and finish with the remaining cheese.

In a small bowl, combine the remaining melted butter with dried onion soup mix, stirring well. Brush this flavorful mixture generously over the tops of the rolls.

Cover the baking dish loosely with aluminum foil and place it in the preheated oven. Bake for 25 minutes. After this time, remove the foil and continue baking for an additional 5 minutes.

While the sliders are baking, prepare the au jus according to the packet instructions. Simply combine the Au Jus gravy mix with water in a saucepan, bringing it to a simmer.

Once baked to perfection, remove the French Dip Sliders from the oven and let them cool slightly before cutting them into individual servings. Serve them warm with the prepared au jus on the side for dipping.