Heat the oven to 375°F (190°C). Cut a circular opening in the top of the loaf, leaving a substantial outer shell and an uncut layer of bread at the bottom. Pull out the interior bread and reserve it for serving or making breadcrumbs.

Melt the butter in a skillet over medium heat. Add the sliced onion and cook for 8–10 minutes, stirring occasionally, until softened and lightly browned.

Add the minced garlic and cook for about 30 seconds, just until fragrant. Stir in the beef broth, dry au jus gravy mix, Worcestershire sauce, kosher salt, and black pepper.

Simmer the seasoned broth mixture for 2–3 minutes. Taste and adjust the seasoning if needed, then reserve some of the hot liquid in a bowl for dipping.

Lightly toast or butter the inside of the hollowed loaf if desired, using the residual butter from the skillet. This creates a helpful barrier against the au jus and meat juices.

Layer half of the provolone inside the bread boat. Add the deli roast beef and cooked onions, then finish with the remaining cheese on top.

Replace the bread top or cover the loaf loosely with foil. Bake for 15–20 minutes, until the cheese is fully melted and the bread is crisp.

Let the bread boat rest for 5 minutes before slicing it into wedges. Sprinkle with chopped parsley if desired and serve immediately with the hot au jus on the side.