Japanese Onion Soup

If you are interested in trying onion soup with a Japanese twist, be sure to check out this Japanese Onion Soup recipe. You will love the harmony between the delicate flavor of onions and the traditional elements of Japanese cuisine.

Japanese Onion Soup is a simple dish made by adding onions to dashi broth and seasoning it with salt and soy sauce. While onion soup is well-known around the world as a French-style dish, typically made with bouillon and butter, in Japan, it is also enjoyed with dashi. The use of dashi gives the soup a light yet umami-rich flavor.

Dashi is a traditional Japanese broth typically made from ingredients such as kombu (dried kelp), bonito flakes (katsuobushi), dried anchovies, or shiitake mushrooms. Various types of dashi can be used, but I recommend bonito dashi for this soup. The umami component in bonito dashi, inosinic acid, pairs well with glutamic acid, the umami component found in onions, enhancing the overall depth of flavor. This combination of umami components provides a rich and savory taste characteristic of Japanese cuisine.

When using bonito dashi for onion soup, there is one thing to keep in mind: if you prepare it using the standard method or use granulated dashi or dashi packets, the dashi flavor can become too strong and overpower the delicate taste of the onions.

Therefore, when making this soup with bonito dashi, it is best to use ichiban dashi (first-brew dashi) prepared with a moderate amount of bonito flakes. This method allows you to extract the umami from the bonito flakes while keeping the flavor light and well-balanced.

Ichiban dashi refers to a broth made by steeping bonito flakes in hot water rather than boiling them. You might be unfamiliar with the term or assume the process is complicated, but rest assured—it is actually quite simple.

The recipe includes instructions for making ichiban dashi, but if you’d like to learn more, please refer to the page on "How to Make Bonito Dashi."

In Japan, when people mention "Japanese onion soup," they are often referring to a dish similar to this recipe. However, if you are simply looking for a Japanese soup that includes onions, I recommend trying miso soup or suimono (a Japanese clear soup where the ingredients are the main focus).

Both are traditional Japanese soups that can incorporate onions, so if you are curious, give them a try.

Ingredients

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Instructions

🕒 Total: 15 mins mins

If you already have bonito dashi (ichiban dashi) or another type of dashi, start from step 3. In that case, use 1 ⅔ cups (400 ml) of your dashi for 2 servings.

Step 1
Put water in a pot and bring it to a boil. Once boiling, turn off the heat and add bonito flakes. Let it steep for 2 minutes.

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Step 2
Strain the mixture through a sieve lined with paper towels or a cloth (such as cheesecloth). Alternatively, if you don't mind some fine bonito flakes remaining, you can simply use a fine-mesh strainer. Bonito dashi (ichiban dashi) is now ready.

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Step 3
Slice the onion into bite-sized pieces. Thinly slice the green onion.

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Step 4
Return the dashi to the pot and bring it back to a boil. Once it boils, add the onion slices and simmer over low heat for 5 minutes. Then, turn off the heat, add salt and soy sauce, and let the flavors meld.

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Step 5
Serve in individual bowls and top with the green onions.

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To store

You can store it in the refrigerator for up to 2 days.