Vietnamese Crab Udon Soup in a Bright Tomato Broth

Vietnamese-inspired crab udon soup brings chewy wheat noodles and tender crab-pork cakes together in a light tomato and fish-sauce broth, finished with fresh herbs and lime. It borrows the tomato, crab, and savory seasoning notes of Vietnamese crab noodle soups, while udon makes this version a satisfying fusion bowl; family and regional versions of Vietnamese crab soups vary.

Ingredients

12 oz (340 g) dried udon noodles
8 oz (225 g) lump crabmeat, picked over for shell and well drained
4 oz (115 g) ground pork
1 large egg (about 50 g, without shell)
2 tbsp (12 g) thinly sliced scallions, plus 2 tbsp (12 g) more for serving
2 tbsp (30 ml) fish sauce, divided
1 tsp (3 g) cornstarch
¼ tsp (0.5 g) ground black pepper, divided
1 tbsp (15 ml) neutral cooking oil
1 medium yellow onion (about 150 g), thinly sliced
3 garlic cloves (about 9 g), finely chopped
1 tbsp (6 g) finely grated fresh ginger
2 medium ripe tomatoes (about 300 g), cut into bite-size wedges
6 cups (1.4 L) low-sodium chicken stock
1 tsp (4 g) granulated sugar
½ tsp (3 g) fine salt, plus more to taste
2 cups (200 g) fresh bean sprouts
½ cup (15 g) mixed fresh mint and cilantro leaves
1 lime (about 60 g), cut into wedges

Instructions

Prepare the crab mixture. In a medium bowl, gently combine the drained crabmeat, ground pork, egg, 2 tablespoons of sliced scallions, 1 tablespoon (15 ml) of the fish sauce, cornstarch, and half of the black pepper. Fold rather than mash: keeping some crab in visible pieces gives the cakes a better texture. Shape the mixture into eight small, evenly sized cakes, about 2 inches (5 cm) across. Set them on a plate while you prepare the pot; there is no need to chill them.
Brown and cook the cakes. Heat the oil in a wide, heavy pot or deep skillet over medium heat. Add the cakes in a single layer, working in batches if needed, and cook for about 4 to 5 minutes per side. Turn them carefully with a thin spatula so they stay intact. The crab is already cooked; USDA FSIS lists 145°F (63°C) as the safe minimum for seafood, and the ground pork and egg in these cakes require 160°F (71°C). Check the center of a cake with a food thermometer and continue cooking as needed to reach 160°F (71°C). Transfer the cooked cakes to a clean plate. They will finish warming in the broth later.
Build the tomato broth. Pour off excess fat if the pot has more than a thin film left. Add the onion and cook, stirring, for about 2 minutes until it starts to soften. Stir in the garlic and ginger for 30 seconds, just until fragrant. Add the tomato wedges and cook for 2 minutes, turning them gently so they begin to release juice without collapsing completely.
Simmer the soup. Pour in the chicken stock and add the remaining 1 tablespoon (15 ml) fish sauce, sugar, salt, and remaining black pepper. Bring the broth to a gentle boil, then lower the heat and simmer for 12 minutes. Taste the broth. Add a little more fish sauce for savoriness or salt if it tastes flat; the right balance should be savory and lightly sweet, with the tomatoes still noticeable. Return the crab cakes to the pot and simmer gently for the final 3 minutes, taking care not to boil them hard.
Cook the udon. While the broth simmers, cook the noodles in a separate pot of boiling water according to the package directions, usually about 3 to 5 minutes for dried udon. Stir once or twice to separate the strands. Drain well. Keeping noodles out of the soup pot prevents them from soaking up too much broth and becoming soft, especially if you expect leftovers.
Assemble and serve. Divide the udon among four deep bowls. Ladle over the hot tomato broth and add two crab cakes to each bowl. Top with bean sprouts, the remaining scallions, mint, and cilantro. Serve lime wedges alongside so each person can add juice to taste. The broth should taste bright and savory, not sharply sour; squeeze in the lime a little at a time.

Tips

Drain the crab well. Excess liquid can make the cakes loose and difficult to turn. If using canned crab, drain it in a fine strainer and gently press it with the back of a spoon. Pick through it with your fingers for shell fragments, even if the package says it has been checked.
Keep the cakes small and handle them gently. Smaller cakes cook through more evenly and are easier to move than one large patty. If a cake begins to break while turning, let it cook another minute before trying again; a browned underside usually releases more cleanly. Use a thermometer rather than relying only on color, since the crab can make the center look pale even when it is cooked.
Choose udon that suits your schedule. Dried noodles are easy to portion and work well here. Fresh or frozen udon can be substituted; cook it according to its package directions, then drain. Frozen udon often needs only a short boil, while fresh noodles may need less time than dried ones. Avoid cooking any style in the broth unless serving immediately, because the starch thickens the soup.
Adjust the seasoning in small steps. Fish sauce varies in saltiness, and stock can be more or less seasoned than expected. Start with the listed amount, taste after simmering, and add fish sauce or salt a teaspoon at a time. Lime belongs at the table rather than in the simmering pot, where its aroma would fade.

Serving Suggestions

Serve this soup as a complete lunch or a light dinner, with each bowl holding noodles, broth, two crab cakes, and a generous handful of fresh toppings. Put extra lime wedges, bean sprouts, and herbs on the table so everyone can adjust the crunch and acidity. A small dish of sliced fresh chile is useful for people who want heat, while leaving the main pot mild keeps the tomato and crab flavors easy to taste.

If you want something alongside it, choose a simple side that will not compete with the broth: a plate of cucumber slices, lightly dressed greens, or steamed vegetables works well. The soup is filling, so a large additional starch is usually unnecessary. Serve it as soon as the noodles are drained and the cakes are hot; udon has its best springy texture just after cooking.

Variations

Use shrimp instead of pork. Finely chop 4 ounces (115 g) of raw peeled shrimp and mix it into the crab mixture in place of the ground pork. Keep the egg and cornstarch as binders, shape the cakes gently, and cook them until the centers reach 145°F (63°C) for seafood; if you also include egg in the mixture, cooking the cakes to 160°F (71°C) is the more conservative target. Shrimp gives the cakes a springier, sweeter bite.

Make a more distinctly Vietnamese-style broth. A small amount of mam tom, fermented shrimp paste, is a traditional ingredient in some Vietnamese crab noodle soups, though recipes differ by region and household. If you can find it, stir ½ teaspoon (about 3 g) into the broth and taste before adding more; it is pungent and salty. If it is unavailable, use the fish sauce already in the recipe rather than trying to reproduce its exact flavor. The result will be cleaner and less funky, but still savory.

Change the noodles or make it spicy. Rice vermicelli is a natural alternative if you would rather move closer to the texture of Vietnamese noodle soups; cook and drain it separately according to the package. For a spicy bowl, add sliced fresh chile at serving or stir a little chile oil into individual portions. Avoid adding a large amount of chili sauce to the whole pot until you have tasted it, since some sauces are quite salty.

Storage and Reheating

For the best texture, store the broth and crab cakes separately from the noodles and fresh garnishes. Refrigerate everything within 2 hours of cooking, using shallow, covered containers so it cools promptly. The broth and cakes keep for 3 to 4 days in the refrigerator; cooked udon is also best used within 3 to 4 days, though it may become softer as it sits. Keep bean sprouts and herbs separate and use them within a few days, following their package or produce condition.

Reheat only the amount you plan to eat. Warm the broth and cakes in a saucepan over medium-low heat, stirring gently, until hot throughout; leftovers should reach 165°F (74°C), checked with a food thermometer. Add a splash of stock or water if the broth has reduced. Reheat noodles briefly in boiling water or place them in the bowl and pour the hot soup over them. Freezing is possible for the broth and cakes for up to 2 months, but the cakes may soften and the tomatoes may lose some texture. Thaw overnight in the refrigerator and reheat to 165°F (74°C); cook fresh noodles and add fresh garnishes after reheating.

Frequently Asked Questions

Can I use imitation crab? Yes. Chopped imitation crab is already cooked and can replace the lump crab in the cakes, though it is usually sweeter and less delicate. Check the label for saltiness, and reduce the fish sauce slightly if the mixture or broth tastes too salty. Imitation crab can be softer, so fold it in gently and keep the cakes small.

Can I use cooked crabmeat from a container? Yes, provided it has been kept refrigerated and is within its use-by date. Drain it thoroughly and check for shell. This recipe assumes cooked crabmeat, not raw crab; cooking the patties to the specified temperature also ensures the ground pork and egg are safely cooked.

Can I make the soup without pork? You can, but the cakes will be more fragile and will not have the same savory, tender texture. For a pork-free option, use an equal amount of finely chopped raw shrimp as described in the variations, or make small crab cakes with an extra teaspoon (3 g) of cornstarch. Handle them gently and check their temperature with a thermometer.

Why cook the noodles separately? Udon releases starch as it cooks and continues to absorb liquid while sitting in broth. Separate cooking keeps the soup clearer and preserves more of the broth for serving. It also makes leftovers easier to store, since you can reheat the broth without turning the noodles overly soft.

Can I prepare any part ahead? You can mix and shape the cakes up to one day ahead, cover them, and refrigerate them promptly. Keep raw pork and egg mixture refrigerated until you are ready to cook; do not leave it at room temperature while preparing the broth. You can also make the broth ahead and refrigerate it for up to 3 to 4 days, then reheat it and cook the noodles just before serving.

What if my broth tastes too salty or too strong? Add a little unsalted stock or water and taste again, rather than adding sugar to mask the salt. If the broth tastes mild, add fish sauce in small increments. Finish with lime in the bowl; a little acidity can make the flavors feel more balanced without changing the salt level.

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Safety notes: safe minimum internal temperatures from USDA FSIS; raw and undercooked fish guidance from the U.S. FDA. Food safety notes

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