Spicy Vietnamese Soup: Lemongrass Beef Noodle Recipe

Spicy Vietnamese soup is a fragrant beef-and-rice-noodle bowl inspired by bún bò Huế, the central Vietnamese soup known for lemongrass, chile, and savory shrimp paste. This home-style version simmers beef bones and chuck into a rich broth, then serves it with noodles and fresh herbs; the heat is adjustable, and regional and family versions vary.

Ingredients

2 lb (900 g) beef chuck, cut into large 2-inch (5-cm) pieces
2 lb (900 g) beef soup bones, such as knuckle or marrow bones
12 cups (2.8 L) water, plus more for blanching
2 stalks lemongrass (about 6 oz/170 g), tough outer leaves removed and stalks bruised
1 medium yellow onion (about 8 oz/225 g), peeled and halved
1 piece fresh ginger, 3 inches (7.5 cm; about 2 oz/55 g), sliced
2 tablespoons (30 ml) fish sauce, plus more to taste
1 tablespoon (15 g) fine salt, plus more to taste
1 teaspoon (4 g) granulated sugar
1 tablespoon (15 g) Vietnamese fermented shrimp paste (mắm ruốc)
1/3 cup (80 ml) neutral oil, such as canola or sunflower oil
1 tablespoon (8 g) annatto seeds, optional, for color
1 to 2 tablespoons (8–16 g) crushed dried chile flakes, to taste
1 tablespoon (15 ml) fish sauce for the chile oil
1 lb (450 g) dried thick round rice noodles, labeled bún bò Huế noodles if available
4 cups (120 g) bean sprouts
2 cups (60 g) loosely packed Thai basil leaves
1 cup (30 g) cilantro leaves and tender stems, roughly chopped
4 scallions (about 60 g), thinly sliced
2 limes (about 120 g), cut into wedges
2 fresh red chiles (about 20 g), thinly sliced, optional

Instructions

Blanch the bones and beef. Put the bones and chuck in a large stockpot and cover with cold water. Bring to a boil over high heat and boil for 5 minutes, skimming any foam. Drain, discard the blanching water, and rinse the pot and the meat under cool running water to remove loose residue. This quick step gives the finished broth a cleaner flavor; it is not a substitute for fully cooking the beef.
Start the broth. Return the blanched bones and beef to the clean pot and add 12 cups (2.8 L) fresh water. Add the lemongrass, onion, and ginger. Bring just to a boil, then lower the heat until the liquid barely simmers. Partially cover and cook for 2 hours 15 minutes, skimming the surface occasionally and adding a little hot water if needed to keep the bones mostly submerged. A gentle simmer helps keep the broth clear and prevents the meat from drying out.
Prepare the spicy seasoning while the broth simmers. Warm the neutral oil in a small saucepan over low heat. If using annatto, add the seeds and warm for 2 to 3 minutes, stirring, until the oil turns orange-red; remove the seeds with a slotted spoon. Take the pan off the heat, stir in the chile flakes, and let them sizzle gently for about 30 seconds. Do not let them brown or burn. Stir in 1 tablespoon (15 ml) fish sauce and set the chile oil aside. For a milder soup, start with 1 tablespoon chile flakes and serve extra at the table.
Check and remove the beef. Lift out a piece of chuck and check its thickest part with a food thermometer. USDA FSIS lists 145°F (63°C) with a 3-minute rest as the safe minimum for whole cuts of beef; for this soup, continue simmering until the beef is also fork-tender, which may take longer. Transfer the beef to a plate and let it rest for at least 3 minutes before cutting it across the grain into bite-size slices. Keep the bones simmering while you finish the broth. Discard the cooked aromatics.
Season and strain the broth. Strain the broth through a fine-mesh sieve into a clean pot, discarding the bones and solids. In a small bowl, whisk the shrimp paste with a ladleful of hot broth until smooth, then stir it into the pot. Add 2 tablespoons (30 ml) fish sauce, the salt, and sugar. Bring the broth back to a gentle simmer for 5 minutes, then taste. Add fish sauce or salt in small increments; shrimp paste is already salty, and its strength varies by brand. Stir in some chile oil if you want the whole pot spicy, or keep the broth mild and let diners add it themselves.
Cook the noodles. Prepare the rice noodles according to the package directions, since soaking and cooking times vary by thickness. Drain them well and rinse briefly with warm water to remove excess surface starch. Avoid cooking them in the broth: that can make the soup cloudy and leaves the noodles more likely to turn soft in the bowl.
Build and serve the bowls. Divide the noodles among six large bowls and top with sliced beef, bean sprouts, basil, cilantro, and scallions. Ladle the bubbling hot broth over everything. Offer lime wedges, sliced fresh chile, and the remaining chile oil at the table so each person can adjust the sourness and heat.

Tips

Use the lemongrass correctly. Bruise the stalks with the back of a knife to release their aroma, but leave them in large pieces so they are easy to remove. If fresh lemongrass is unavailable, use 2 tablespoons (30 g) frozen minced lemongrass; the broth will be less clean-tasting, so strain it carefully.
Adjust shrimp paste with care. Mắm ruốc brings a distinctive fermented depth associated with bún bò Huế. If you cannot find it, use 1 tablespoon (15 g) white miso mixed with 1 teaspoon (5 ml) fish sauce. This gives the broth savory body but is milder and does not reproduce shrimp paste’s aroma. Check labels if avoiding shellfish; shrimp paste contains shrimp.
Keep chile from scorching. Add flakes after removing the oil from the heat, and stir briefly. Burnt chile tastes bitter, so if the oil starts smoking, let it cool before adding the flakes. The oil can be made less hot by using fewer flakes or more fragrant by adding a pinch of paprika, though paprika changes the flavor slightly.
Use a gentle simmer, not a rolling boil. A hard boil can emulsify fat into the broth and make it cloudy. Skim foam early, and season only after straining because the broth reduces a little and the shrimp paste contributes salt.

Serving Suggestions

Serve this soup as a complete meal in wide, deep bowls, with the toppings arranged so they stay visible above the broth. Set out lime, extra herbs, chile oil, and sliced fresh chiles separately: lime brightens the rich beef broth, while herbs add a cool, fresh contrast to the lemongrass and chile. A small dish of fish sauce can be offered for anyone who wants a saltier bowl, but taste first because the broth is already seasoned.

If you are serving a group, keep the broth at a gentle simmer and place noodles and garnishes in separate serving dishes. Ladle broth only when each bowl is ready, rather than letting the noodles sit in the pot. This keeps the noodles springy and allows guests to set their own spice level. A simple side of sliced cucumber or lightly dressed greens works well if you want something crisp alongside the hot soup.

Variations

Make it more like a classic bún bò Huế bowl: Use thick, round rice noodles and include the shrimp paste and lemongrass. Some versions include pork hock, Vietnamese pork sausage, or other cuts of beef; ingredients and toppings vary by household and region. If adding pork hock, simmer it until tender and check that it reaches at least 145°F (63°C) with a 3-minute rest as a whole cut, using a thermometer in its thickest part.

Make a less spicy broth: Leave the chile flakes out of the pot and serve the chile oil on the side. You can also begin with only 1 teaspoon (3 g) flakes, then add more to individual bowls. Fresh red chiles are optional and can be omitted without changing the broth’s basic flavor.

Use another beef cut: Beef shank can replace chuck in the same amount, though it may need extra simmering to become tender. Short ribs make a richer, fattier broth; skim the surface more often. Whichever cut you choose, check safe temperature and tenderness rather than relying only on the clock.

Choose a noodle substitute: If thick round rice noodles are unavailable, use medium-width rice sticks. They are thinner and cook faster, so follow their package directions and expect a less chewy bowl. Avoid wheat noodles if you want the rice-noodle texture associated with this style of soup.

Storage and Reheating

For food safety, refrigerate the broth and beef within 2 hours of cooking. Store them in a covered container, ideally with the beef submerged in broth, for 3 to 4 days. Keep cooked noodles and fresh garnishes separate; noodles are best freshly cooked, but leftovers can be refrigerated in a separate container for up to 2 days, where they may become softer.

Reheat broth and beef on the stovetop until steaming, and use a food thermometer to make sure leftovers reach 165°F (74°C). Heat only the amount you plan to serve. Warm noodles briefly in hot water, drain, and put them in bowls before adding the reheated broth. Freeze broth and beef, without the herbs or noodles, for up to 3 months for best quality; thaw overnight in the refrigerator and reheat to 165°F (74°C). Do not leave the soup at room temperature for more than 2 hours.

Frequently Asked Questions

Is this the same as bún bò Huế?
This is a home-style recipe inspired by bún bò Huế, not a claim to represent every traditional version. It uses the recognizable combination of beef, lemongrass, chile, shrimp paste, and rice noodles, while some versions use different cuts, pork, sausage, or additional toppings.

How can I make the soup spicy without making the whole pot hot?
Prepare the chile oil separately and leave it out of the broth. Serve a small spoonful with each bowl, then add more to taste. This is especially helpful when diners have different preferences or when serving children who prefer a mild soup.

Can I make the broth a day ahead?
Yes. Strain and chill the broth promptly, refrigerating it with the cooked beef for up to 3 to 4 days. The flavors will settle as it rests, and any firm layer of fat on top can be lifted off before reheating if you prefer a leaner-feeling broth. Cook the noodles and prepare the herbs shortly before serving.

What if I cannot find thick round rice noodles?
Medium-width rice noodles are a practical substitute and are widely available. Their texture is less substantial than the thick round noodles, and their cooking time may be shorter, so check the package and taste a strand before draining.

Can I make the broth without shrimp paste?
Yes. Use the white-miso and fish-sauce substitute in the Tips section, or omit the paste and add fish sauce gradually. Without shrimp paste, the broth will still be savory but will lack the fermented, seafood-rich note that distinguishes many versions of this soup.

Why is my broth cloudy?
A vigorous boil can disperse fat and small particles through the liquid. Keep the pot at a low simmer, skim foam during the first part of cooking, and strain the finished broth. Cloudiness does not necessarily mean the soup is unsafe, but a gentler simmer produces a clearer-looking bowl.

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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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