Melt 2 tablespoons of unsalted butter in a skillet over medium heat. Add thinly sliced onions and sauté, stirring occasionally, for 12-15 minutes until they become soft and deeply browned. Stir in fresh thyme, kosher salt, and black pepper, then remove from heat and set aside.

Preheat your oven to 350°F (175°C). Carefully slice the sweet rolls in half without fully separating them and lay the bottom halves in a baking dish, ensuring they fit snugly.

Begin layering your sliders by placing half of the provolone cheese evenly over the bottom halves of the rolls. Then, add the sliced deli roast beef generously on top, followed by the caramelized onions. Finish with the remaining slices of cheese before gently placing the top halves of the rolls over everything.

In a small bowl, mix together the melted butter and a packet of dried onion soup mix until well combined. Brush or pour this mixture evenly over the top of the rolls.

Cover your baking dish loosely with foil and bake the sliders in the preheated oven for 25 minutes. Remove the foil and bake for an additional 5 minutes until golden and bubbly.

While the sliders are baking, mix the Au Jus gravy according to the package instructions with water in a saucepan. Heat gently over medium heat until it reaches a simmer.

Once the sliders are baked to perfection, remove them from the oven and slice them apart. Serve warm with a bowl of Au Jus on the side for dipping.