Place the onion halves and ginger cut-side down in a dry skillet, under a broiler, or directly over a gas flame. Char until deeply browned and lightly blackened in spots. Add the garlic for the final 2–3 minutes so it softens and takes on a little color without burning. This step matters because the onion and ginger need that lightly smoky, sweet, roasted edge that gives the beef a recognizably pho-like base rather than a plain pot-roast flavor. Set aside. Direct charring caramelises the onion's natural sugars and blooms the ginger's aromatic oils in a way gentle sautéing never achieves — that smoky, roasted character is what carries this braise's flavour firmly into pho territory rather than reading as an ordinary beef stew.

Place the star anise, cinnamon stick, coriander seeds, and cloves in a dry pan over medium-low heat for 45–60 seconds, just until fragrant. Do not darken or burn them. The goal is to wake up the oils in the spices, not make them bitter. Set aside. This brief dry toast is enough to release the spices' aromatic oils without pushing them anywhere near the point where those same compounds turn acrid — the window here is short and worth watching closely rather than walking away.

Pat the beef dry and season it all over with the salt and black pepper. Heat the neutral oil in a heavy pot or Dutch oven over medium-high heat. Sear the beef well on all sides until deeply browned. Work in batches if needed so the meat browns rather than steams. The beef should develop a proper crust. That browning is what gives the finished sandwich depth and a richer savory edge once the braising liquid reduces. Remove the beef to a plate. Searing in properly spaced batches, rather than crowding the pot, is what allows genuine contact between the meat's surface and the hot pot — crowded beef releases moisture and simmers rather than developing the dark crust that becomes the foundation of everything the braising liquid builds on afterward.

Lower the heat to medium. Add the charred onion, ginger, and garlic to the pot briefly. Add the toasted spices, fish sauce, soy sauce, and brown sugar. Stir for a few seconds, then pour in the beef stock and water, scraping up everything stuck to the bottom. Return the beef to the pot. The liquid should come about ⅔ of the way up the beef; add a little more water if needed. Bring just to a gentle simmer, then cover with the lid slightly ajar and braise on very low heat for about 2½ to 3 hours, until the beef is fully tender. The liquid should never boil aggressively. A quiet, slow braise keeps the beef tender and lets the spice profile stay clean and aromatic. Keeping the liquid at roughly two-thirds up the beef rather than fully submerging it concentrates the braise's flavour into a smaller volume — a fully submerged braise dilutes both the meat and the eventual jus, producing a thinner result even after the same amount of later reduction.

Lift the beef out of the braising liquid and rest it for 10 minutes. Strain the braising liquid and discard the aromatics and whole spices. Return the strained liquid to the pot and simmer uncovered until slightly reduced and glossy. It should taste concentrated, beefy, lightly sweet, aromatic, and balanced, not watery. Slice the beef thinly against the grain. Return the sliced beef to a little of the reduced braising liquid and toss gently so it stays juicy and lightly glazed. The beef should be moist and richly flavored, not dry, shredded to threads, or swimming in broth. This is a sandwich filling, so it needs to be juicy but controlled. Resting the beef before slicing lets the juices that redistributed through the meat during the long braise settle back evenly rather than spilling onto the board the moment a knife goes in, and reducing the strained liquid separately afterward is what turns a thin braising liquid into something that clings to the sliced beef rather than soaking straight through the bread.

Thinly slice the white onion, scallions, and jalapeños. Pick the cilantro and Thai basil leaves. Measure out the crispy fried shallots and hoisin. Keep the herbs fresh and dry so they stay lively in the sandwich and do not collapse into the hot beef immediately. Prepping every fresh topping fully before the beef is even sliced means the assembly stage moves quickly once the meat is hot and ready, rather than competing with last-minute prep for the person's attention.

Split the baguette sections lengthwise without cutting all the way through if you want a hinged sandwich. If desired, lightly toast the cut sides until just crisp. Do not over-toast. The bread should stay crusty outside but still have enough give inside to hold the juicy beef and toppings without shattering. A light toast gives the baguette real, if modest, resistance against the beef's own moisture and the reduced jus, without pushing the bread toward a harder, more resistant crust that would fight the bite.

Divide the hot sliced braised beef evenly among the 4 baguette sections, about 200g per sandwich. Top each with thin white onion, scallions, cilantro, Thai basil, thin jalapeño slices, and a generous sprinkle of crispy fried shallots. Drizzle hoisin sauce over the top. If the meat needs a little more moisture, spoon over 1–2 tablespoons of the hot reduced braising jus before closing the sandwich. The final sandwich should eat like a bridge between pho and bánh mì: rich beef, aromatic spice, fresh herbs, raw onion brightness, chili heat, and just enough hoisin sweetness to pull it together. Serve immediately. Adding the crispy fried shallots as the very last topping, right before the sandwich closes, protects them from the beef's residual heat and moisture — even a minute or two of earlier contact would soften their defining crunch.