In a medium skillet over medium heat, melt 2 tablespoons of butter and cook the onions until lightly browned and soft. Set aside.
Preheat the oven to 350°F and grease a 9 x 13 baking dish with nonstick cooking spray.
Keeping the Hawaiian sweet rolls attached, run a serrated knife through the middle of the loaf, dividing the top and bottom halves.
Place the bottom half in the prepared baking dish and evenly lay on the cheese.
Scatter on the roast beef, followed by the onions.
Top with the top half of the rolls.
In a small bowl, melt the remaining 8 tablespoons of butter in the microwave (about 15 seconds). Stir in the Au Jus gravy mix, Worcestershire sauce, sesame seeds, garlic powder, and onion powder.
Pour sauce over the rolls and bake until the cheese has melted, about 15 to 20 minutes.
Operating within a tight thirty-minute total window requires building flavor simultaneously across distinct cooking zones rather than sequentially. Onions caramelize via the Maillard reaction when heated gently in fat over medium heat, breaking down complex carbohydrates into simple sugars that balance the salinity of the cured beef and cheese. Originating from the classic Los Angeles roast beef sandwich dipped in pan drippings, this pull-apart adaptation transforms a traditional lone portion into a cohesive batch by utilizing the high sugar content of Hawaiian sweet rolls to counter the rich umami load of the au jus mix and Worcestershire sauce. Combining eight tablespoons of melted unsalted butter with powdered gravy elements creates a temporary emulsion that coats the bread thoroughly before baking at 350 degrees Fahrenheit. Sesame seeds added to the butter mixture introduce a nutty lipid profile and toasted aroma that pierces through the heavy dairy fats of the provolone cheese. Slicing the bread horizontally while keeping the 12 rolls physically attached maintains a uniform structural crumb, preventing the bottom layer from sogging under the heavy roast beef filling. Baking the assembled loaf uncovered for fifteen to twenty minutes achieves complete protein coagulation in the cheese without over-toasting the exterior crust, yielding a molten interior held together by a toasted bread shell.