Pho chay lives or dies on one decision: how hard you roast the vegetables. This is where bones would normally provide depth and body, so the vegetables have to work harder than they usually would. The daikon and mushrooms add umami and weight; the charred onion and ginger provide the characteristic sweetness; the spice sachet anchors everything to the pho lineage. Do not shortcut the roasting step.
The broth
2-3 hours, partially attended
Roast the vegetables
Heat your oven to 220C (425F). Place the daikon, carrots, celery, and mushrooms on a large baking tray. Toss with a thin film of neutral oil. Roast for 35-40 minutes, turning halfway, until the edges are deeply caramelised and beginning to char. They should look more roasted than you are comfortable with -- that colour is flavour.
Char the onion and ginger
Place the halved onions and ginger cut-side-down directly over a gas flame, under a broiler, or in a dry cast iron pan over high heat. Char until the cut surfaces are deeply blackened -- not just browned, actually black in places. About 5 minutes per side. This is the same technique as the beef and chicken versions and equally non-negotiable here. It is the source of sweetness, colour, and complexity.
Toast the spices
In a dry frying pan over medium heat, toast the star anise, cinnamon, cloves, coriander seeds, cardamom, and fennel for 2-3 minutes, stirring frequently, until fragrant and slightly darkened. Do not leave them. Transfer immediately to a muslin sachet or cheesecloth square tied with kitchen string.
Build the broth
Add all the roasted vegetables, charred onion, and ginger to a large pot. Cover with 3 litres of cold water. Bring to a boil, then reduce to a steady gentle simmer. Add the spice sachet. The broth will look quite dark initially from the roasting -- this is correct. It will clarify and mellow as it simmers.
Simmer
Simmer for 2-3 hours. Unlike a meat broth, vegetable broth does not improve indefinitely with time -- after about 3 hours some vegetables can turn bitter. Check and taste at the 2-hour mark. If the broth tastes full and rounded, it is ready to strain. If it still tastes thin, continue for another 30-60 minutes.
If you used dried shiitake, remove and reserve them at the 1-hour mark -- they will have given most of their flavour and can be sliced and used as a bowl topping.
Strain and season
Strain through a fine mesh strainer, pressing the vegetables firmly to extract every drop. Discard the solids. The broth should be a deep amber-brown -- beautiful and clear.
Season with soy sauce one tablespoon at a time, tasting after each addition. Add the rock sugar. If using, stir in the miso paste off the heat -- whisk it with a small ladle of broth first, then add to the pot. Do not boil after adding miso. Adjust salt if needed.
Assembly
15-20 minutes when ready to serve
Prepare the tofu
Press firm tofu between paper towels for 10-15 minutes to remove excess moisture. Cut into 1cm slices or cubes. Pan-fry in a non-stick pan with a little oil over medium-high heat until golden on each side -- about 3-4 minutes per side. Alternatively, bake at 200C for 20-25 minutes, flipping halfway. The exterior should be chewy and golden; the interior soft. Season lightly with salt while still hot.
Prepare the mushroom topping
If using fresh shiitake, thinly slice the caps and saute in a little oil with a pinch of salt over high heat for 3-4 minutes until golden and slightly chewy. If using the reserved rehydrated dried shiitake from the broth, simply slice them -- they are already cooked and full of flavour.
Prepare the noodles
Soak the dried banh pho in cold water for 30 minutes if not already done. Bring a separate pot of plain water to a rolling boil. Cook the noodles in batches in a wire strainer for 1-2 minutes until just tender. Drain immediately.
Bring the broth to a full boil
Return the strained and seasoned broth to a vigorous boil before ladling. Taste one final time. The seasoning at boiling temperature will taste slightly different from when it was cooling -- adjust as needed.
Build the bowl
Place a portion of hot noodles in a warmed bowl. Arrange the golden tofu and sliced mushrooms on top. Ladle boiling broth generously over everything. Finish with thinly sliced spring onion. Serve the herb plate alongside with lime, fresh chili, bean sprouts, and Thai basil.
Notes and variations
Umami builders
Dried shiitake are the single biggest flavour contributor in vegetarian pho. Do not substitute with fresh shiitake for the broth -- the dried version has a concentrated depth that fresh mushrooms cannot match. Kombu seaweed added in the last 30 minutes also adds significant body.
Make it ahead
The broth keeps refrigerated for 5 days and freezes well for 3 months. Unlike chicken, there is no meat component to worry about -- freeze the broth in portions and you can have a bowl ready in 20 minutes any evening.
Tofu alternatives
Fried tofu puffs (dau hu ky) from an Asian grocery store are exceptional in pho chay -- they soak up the broth without losing structure. King oyster mushrooms, sliced and seared, are another excellent protein. A combination of all three makes an extraordinary bowl.
Vegan fish sauce substitute
Some pho chay recipes use a vegetarian fish sauce made from seaweed and mushrooms. If you can find it, use it in place of the soy sauce -- the flavour profile is closer to the original. Several Vietnamese brands make a good version.
The roasting shortcut
If you are short on time, char the onion and ginger as instructed (this takes 10 minutes and cannot be skipped) and simmer the unroasted vegetables for 3 hours with a generous handful of dried shiitake. You lose some depth but gain an hour.
Buddhist temple style
Traditional Vietnamese Buddhist pho chay avoids alliums entirely -- no onion, garlic, spring onion, or chives. The broth relies entirely on vegetables, mushrooms, and spices. It is a fascinating constraint that produces a surprisingly complex result.