Vietnamese Water Spinach and Pork Noodle Soup (Canh Bún)

Traditional Canh Bun

Traditional Canh Bún (and Bún Riêu) features a broth made with tomatoes and field paddy crab (cua đồng), resulting in a light yet flavorful soup.

Rice field paddy crabs are small with very little meat, so they are crushed whole, shells and all, and boiled. The crab meat that floats to the surface is gathered and served as a topping (crab cake), and the strained liquid from crushing the crab is used as the stock.

Modern Canh Bun

Since fresh field paddy crabs are hard to come by in the United States and really anywhere outside of Vietnam, many modern adaptations rely on canned spiced crab and using pork bones for a heartier broth.

For this recipe, we are adapting the soup using a hearty pork-based broth, similar to how Bún Riêu is adapted in the West.

Canh Bun vs. Bun Rieu

I like to think of Bún Riêu as the fancier version, while Canh Bún is the everyday version. It is much simpler, easier to prepare, and requires fewer accompaniments.

The Key Differences

• No crab cake/meatball: Canh Bún is much simpler, so we completely skip the riêu (the crab meatball or crab cake topping). Other recipes might still keep the riêu, but why not just call it Bun Rieu at this point?
• Noodles: Canh Bún typically uses thicker rice noodles (the same ones used for spicy Vietnamese noodle soup Bún Bò Huế). Bún Riêu uses thinner vermicelli noodles, like the ones in noodle salad, Bún Thịt Nướng.
• Water spinach, also known as morning glory (Rau Muống): Canh Bún incorporates cooked water spinach, simply chopped and boiled. Bún Riêu uses thinly shredded water spinach and it’s served raw on the side. It also served with an assortment of other vegetables and herbs, such as bean sprouts and shredded banana blossom.
• Garlic Chives (Hẹ): Canh Bún uses garlic chives for the garnish instead of green onions.

What You Need to Make Canh Bun

To make my easy version of Canh Bun, gather the following ingredients:

• Pork Bones: I’m using large pieces of pork neckbone and shank bones. Because my husband is allergic to shrimp, this recipe skips the dried shrimp that is also simmered with the bones. Feel free to include them but the pork bone broth is flavorful enough to stand completely on its own and husband lives.
• Tomatoes: You can’t go without tomatoes. They add a tangy sweetness to the broth and a beautiful splash of color. Use whatever tomatoes you like, just make sure they are ripe. You can cut them into smaller pieces or leave them in larger chunks. I have kids who hate tomatoes, so I chop them into small pieces. That way they can’t fish them out (evil laugh).
• Annatto Seeds: This is the secret to giving the broth its signature red color. You can buy pre-made annatto oil or easily make it yourself by rendering whole annatto seeds in hot neutral oil until the oil turns a deep reddish-orange, then discarding the seeds. If you don’t have it, you can use a bit of tomato paste mixed into the broth. Or you can leave it out entirely since it doesn’t add anything other than color, though your broth might look a bit dull without it.
• Fried Tofu: These act like delicious little sponges, absorbing the flavors of the broth. If you can’t find fried tofu, you can make themselves by frying firm tofu with a bit of oil until golden on all sides. Just make sure to drain out any excess water by squeezing it gently with paper towels before frying.
• Morning Glory / Water Spinach (rau muong / ong choy): The vegetable of Canh Bun. Keep in mind that it can get quite expensive during the winter months here in California. A great, crunchy, budget-friendly alternative is to use thinly sliced celery.
• Thick Rice Vermicelli Noodles: These are the round rice noodles (the same kind you would buy for Bún Bò Huế).
• Seasonings: Fish sauce, salt, and a touch of sugar to turn the stock into a flavorful broth. I’m also using MSG to make it awesomely delicious. You can omit MSG if preferred.
• Shrimp Paste (mam tom or mam ruoc): This is typically served on the side as an optional flavor enhancer. You can use whichever variety you can find. I am using Mam Ruoc.
• Herbs and Aromatics: Fresh garlic, shallots (or sub with yellow onions), garlic chives (hẹ), fresh red chilies, and lime wedges.
• Fried Fish Cake or Fried Pork Roll (cha chien): You can skip if your pork bones already have generous amounts of meat on them, but if you prefer more meat, this is a delicious and easy topping. You can get them already made. I like to get it raw by purchasing pork paste or fish paste from Duc Huong sandwich shop that comes in a tub and pan frying it myself.

How to Make Canh Bun

Step 1: Make the Pork Stock

Many home cooks parboil the pork bones to remove impurities (the gunk that comes out of the bones), but you can skip this step. We just have to do a bit more skimming during cooking.

If you do skip it, like me, give them a good clean with hot water from the faucet until the water runs clear.

Add the washed pork bones and water to a large pot (at least 5 quart capacity), along with peeled shallots.

Simmer for one hour. Skim the surface as needed as impurities rise to the top to keep the stock clear. A clear broth is a happy broth in Vietnamese cooking.

Step 2: Prepare Tomatoes

While the pork bones are simmering, In a separate pan, prepare the tomatoes. Start with adding neutral oil and annatto seeds. Gently heat until seeds just start to blacken.

Discard seeds and leave the oil. Add finely minced garlic and shallot into the annatto oil. Sauté until fragrant then add tomatoes and pan fry to release their subtle red color and sweetness.

Add this mixture to your stock, making sure to get all the last bit of annatto oil for that gorgeous color.

Step 3: Cook the Noodles

Cook the vermicelli according to package instructions. Drain and rinse with cold water to prevent sticking then set aside.

Step 4: Add Seasonings and Tofu

Back to the stock. Once it is done cooking and the pork meat is tender (it can easily be pierced with a chopstick), season to taste with salt, fish sauce, sugar and MSG (optional). Add a little at a time, to taste. Add the fried tofu to the pot. Broth is done!

Step 5: Prepare Accompaniments

Cut or snip with your fingers the water spinach into 2-inch segments. You want both stems and leaves. Wash well then quickly boil the water spinach in a small amount of water (about a minute). Drain, rinse with cold water, and set aside.

Step 6: Serve

In a bowl, combine noodles, blanched morning glory, fresh garlic chives, and a couple of ladles of hot pork broth. Add fried pork or fish cake and pork bones.

Pro Tips & FAQs

Level up mắm ruốc

You can use it directly from the jar, but if you want to level it up, use the same prepared mắm ruốc recipe I use for tart unripe green mangoes. It’s a lot more fragrant and flavorful than using it straight from the jar.