II
The Method
1
Place all bones in a large pot. Cover with cold water. Bring to a vigorous boil and boil hard for 3–5 minutes. Drain. Rinse every bone under cold running water, scrubbing away any grey residue. The bones are ready when the rinsing water runs clear.
2
Char the ginger and onion. Hold the ginger halves and onion halves cut-side-down directly over a gas flame, or place cut-side-up under a very hot grill. Char until the cut surfaces are blackened in patches — not uniformly carbonised, but mottled with deep colour. The smell shifts from raw allium to something smoky and caramelised: that is the signal to remove them.
3
Toast the spices. In a dry pan over medium heat, toast the star anise, cinnamon stick, cloves, black cardamom, fennel seed, and coriander seed together, shaking the pan, until fragrant — approximately 90 seconds. The spices darken slightly and the room fills with the combined aroma of anethole and warm resin. Tie them in a piece of muslin.
4
Place the blanched bones in a very large clean pot. Add 4–5 litres of cold water. Bring slowly to a simmer. During the first 30 minutes, skim the surface continuously with a ladle — grey foam will rise in successive waves. Continue skimming until no further foam appears and the surface is clean. The broth is ready for the aromatics when the surface is quiet and clear.
5
Add the charred ginger, charred onion, the spice bundle, and the rock sugar. Reduce the heat to the lowest setting that maintains movement in the pot. This is where the dish lives or dies: the simmer must be barely perceptible — a single bubble breaking the surface every few seconds, never a rolling or active simmer. Collagen converts to gelatin at any temperature above 70°C; it is temperature control, not violence of heat, that produces a clear broth. Maintain this temperature for 6–8 hours without interruption. A vigorous simmer produces a cloudy, inferior broth regardless of skimming.
6
Thirty minutes before the end of the cooking time, season with 40–50 ml of fish sauce. Taste: the broth should read as deeply beefy, slightly sweet from the rock sugar and charred onion, with the spice aromatics present as a background. The fish sauce provides salt — it should be noticeable but not dominant. Adjust within the stated range.
7
Strain the broth through a fine-mesh sieve lined with muslin into a clean pot. Discard bones, aromatics, and the spice bundle. The finished broth should be clear to amber, with no grey turbidity. When a ladle is lifted, the broth should fall back in a slightly viscous sheet — thicker than water, from the dissolved gelatin. If it falls as thin as water, the knuckle collagen has not fully converted and the broth required longer time.
8
To serve: place cooked bánh phở noodles in warmed deep bowls. Arrange slices of raw beef over the noodles. Ladle the broth at a full rolling boil directly over the raw beef — the heat of the broth cooks the slices in the bowl. The beef is done when it has just turned from red to pale pink, which occurs within seconds of contact with the hot broth. Bring the table garnishes to the table separately.