1. Caramelize the Onions: Sweet and Savory Depth

1. Melt Butter: In a large skillet, melt 3 tablespoons of unsalted butter over medium heat.
2. Add Onions: Add the thinly sliced onions to the skillet and coat them in the melted butter.
3. Cook Slowly: Cook the onions, stirring occasionally, for about 12-15 minutes. The goal is to soften and caramelize them, bringing out their natural sweetness. They should be a light golden brown but not burnt.
4. Add Seasonings: Add the minced fresh thyme, salt, and pepper to the onions. Stir to combine everything well.
5. Set Aside: Remove the skillet from the heat and set the caramelized onions aside.

2. Prepare the Baking Dish and Rolls: Setting the Stage

1. Preheat Oven: Preheat your oven to 350°F (175°C).
2. Slice Rolls: Take the sweet rolls out of the package, but do not separate them. Keeping them connected, use a large, sharp knife (like a bread knife) to slice horizontally through all the rolls at once, creating a top and bottom half.
3. Place in Dish: Place the bottom half of the rolls, cut-side up, into an 11×7 inch baking dish.

3. Assemble the Sliders: Building Layers of Flavor

1. Layer Cheese: Top the bottom layer of rolls with half of the provolone cheese slices (about 5 slices), overlapping them slightly if needed.
2. Add Roast Beef: Evenly distribute the sliced deli roast beef over the cheese layer.
3. Top with Onions: Spread the caramelized onions evenly over the roast beef layer.
4. Add Remaining Cheese: Top the onions with the remaining provolone cheese slices.
5. Add Top Buns: Place the top half of the sweet rolls over the cheese layer, aligning them with the bottom halves.

4. Prepare the Topping: A Buttery, Flavorful Glaze

1. Melt Butter: In a small bowl, melt the remaining ½ cup of unsalted butter.
2. Combine with Onion Soup Mix: Stir the dried onion soup mix into the melted butter until it’s well combined.

5. Brush and Bake: Creating a Golden-Brown Finish

1. Brush with Butter Mixture: Using a pastry brush, generously brush the melted butter and onion soup mix over the tops of the rolls. Make sure to coat the entire surface evenly.
   • Tip: If you don’t have a pastry brush, you can carefully pour the butter mixture over the rolls.
2. Cover Loosely: Cover the baking dish loosely with aluminum foil.
   • Tip: Make sure the foil is not touching the tops of the rolls directly, or they may stick.
3. Bake: Bake for 25 minutes covered.
4. Uncover and Bake: Remove the foil and bake for an additional 5 minutes, or until the tops of the rolls are golden brown and the cheese is melted and bubbly.  

6. Prepare the Au Jus: A Rich and Savory Dipping Sauce

1. Combine Ingredients: While the sliders are baking, prepare the au jus. In a medium saucepan, combine the au jus gravy mix with the 3 cups of water.
2. Bring to a Boil: Bring the mixture to a boil over medium-high heat, whisking constantly.
3. Simmer: Once boiling, reduce the heat to low and simmer for about 5 minutes, or until the au jus has thickened slightly, whisking occasionally.
4. Serve: Remove from heat.

7. Cool, Garnish, and Serve: The Final Touches

1. Cool Slightly: Let the sliders cool for a few minutes in the baking dish.
2. Garnish (Optional): If desired, sprinkle the tops of the sliders with freshly chopped parsley for a pop of color and freshness.
3. Serve with Au Jus: Serve the French Dip Sliders warm, with the hot au jus on the side for dipping.