Pat the chuck roast dry. Mix kosher salt, black pepper, paprika, garlic powder and onion powder and rub all over the roast. Heat olive oil in a large heavy‑bottomed Dutch oven or skillet over medium‑high heat. When shimmering, sear the roast 3–4 minutes per side until deeply browned. Transfer roast to a plate.

Caramelize onion

Slice the yellow onion into 1/2" wedges. Reduce heat to medium, add a touch more oil if needed, add onions and cook 6–8 minutes until softened and starting to brown, scraping up browned bits from the pan.

Braise or smoke-roast

Return the roast to the pot. Add beef broth and soy sauce/Worcestershire (and the optional extra tablespoon Worcestershire if using). The liquid should come about 1/3 to 1/2 up the side of the roast. Bring to a simmer, cover, and transfer to a 300°F (150°C) oven and braise 3–3.5 hours until the beef pulls apart easily. Alternatively: for a smoked profile, smoke the roast at 225–250°F until internal temperature reaches 190–205°F (about 6–8 hours depending on size), then transfer to a covered pan with 1–1.5 cups beef broth and finish in a 300°F oven until fork‑tender.

Shred and collect drippings

Remove roast to a cutting board and let rest 10 minutes. Using two forks or meat claws, shred the beef into large shreds. Skim fat from the cooking liquid in the pot and reserve pan drippings. Return shredded beef to the pot with the braising liquid and onions and simmer gently 10–15 minutes to marry flavors. Season to taste with salt and pepper.

Make pan‑dripping gravy (debris)

Melt unsalted butter in a small saucepan over medium heat. Whisk in the flour to make a blonde roux, cook 1–2 minutes without browning. Slowly whisk in 1 to 1.5 cups of the reserved braising liquid (adjust for desired thickness) until smooth. Cook until thickened, 3–5 minutes. Taste and adjust seasoning with salt, pepper, and a splash of Worcestershire if needed. Pour gravy back into the pot with shredded beef and stir—this will produce the characteristic soul-saturating 'debris' (loose bits in gravy). Keep warm on very low heat.

Onion Aioli

In a small bowl combine mayonnaise, mustard, lemon juice, minced garlic, finely minced shallot, and the finely minced red onion. Stir until smooth. Season with salt, black pepper and optional hot sauce. Taste and adjust acidity or seasoning. Refrigerate at least 20 minutes to let flavors meld. (Aioli can be made up to 24 hours ahead.)

Assembly & Toppings

Prepare bread

Preheat oven broiler or a skillet. Slice each French loaf lengthwise, leaving a hinge if you prefer. Brush cut sides lightly with melted butter. Toast cut sides under the broiler 1–2 minutes or in a skillet over medium heat until lightly golden.

Assemble Po' boys

Spread a generous layer (about 1–2 tbs) of onion aioli on both cut sides of each toasted roll. Pile warm shredded beef with plenty of gravy (about 3/4 to 1 cup beef mixture per sandwich) onto the bottom half of each roll so the bread soaks up 'debris.' Top with lettuce leaves and tomato slices and add pickles if using. Close sandwich, press lightly to absorb juices.

Serve

Serve immediately while beef is hot and gravy is saucy. Provide extra gravy in a small bowl for dipping or to spoon over sandwiches. Leftover debris stores in refrigerator 3–4 days and reheats gently on the stove with a splash of broth.