Japanese Steakhouse Onion Soup Made Vegetarian

A Japanese Steakhouse Onion Soup for Vegetarians- Clear, Comforting, and Unami-Rich

I know it’s summer in the US, but I still eat soup in the summer. If you don’t, then tuck this recipe away for the fall. If you live in Australia- this is perfect timing I think!

If you have ever eaten in an American Japanese Hibachi style steakhouse, your first course may have been a small bowl of clear onion-based soup that was light, warm, and full of onion flavor.  Americans have come to know this type of soup as Japanese onion soup. 

🌸 Where Did Japanese Onion Soup Originate?

Surprisingly, this soup has no history in Japanese homes. The kind of onion soup we see in American Japanese restaurants became popular in the 1960s and 70s. Restaurants such as Benihana (a popular Japanese Hibachi steakhouse chain) served Japanese onion soup as a starter before the main meal.

It is an easy soup that offers a flavorful clear broth and is usually topped with onions, mushrooms, and scallions. Even though the recipe has no history in Japan, it was inspired by authentic Japanese cooking — especially the idea of keeping flavors simple and clean.

🍜 How People Eat in Japan

In Japan, people do eat clear soups — called osuimono — but they aren’t usually onion-based. They are sometimes dashi or seafood based. 

So while the onion soup served in a Japanese steakhouse isn’t actually traditional, it still aligns with the Japanese cooking style. 

💚 Why This Kind of Soup is Popular

Most people enjoy this simple soup. It’s not heavy, it’s warm, and it makes a great starter before a large meal. Although it is usually made with beef or chicken broth, it’s easy to make this vegetarian version which still tastes rich and satisfying. 

 Easy Vegetarian Japanese Onion Soup Recipe

Ingredients:

• 2 medium yellow onions, thinly sliced

• 2 cloves garlic, minced

• A small piece of fresh ginger, sliced

• 4 cups of vegetable broth and 1 cup water

• 3 dried shiitake mushrooms and 1 piece of kombu seaweed

• 1-2 tablespoons tamari

• 1-2 teaspoons mirin (optional, for a hint of sweetness)

• 2 stems of green onion, chopped for garnish

• A few fresh baby portobello mushrooms, sliced and sautéed for garnish (optional)

• Salt to taste

Steps:

1. Make the onion broth:

   • Put the vegetable broth, water, kombu, and dried shiitake mushrooms in a pot.

   • Let it sit for 30 minutes (no heat yet — just soaking).

   • After soaking, bring it to a light simmer.

   • Remove the kombu once the broth starts to bubble (boiling it too much can make it slimy).

   • Let the dried mushrooms simmer for an additional 10-15 minutes, then remove them as well (you can slice and use them later if you want).

2. Cook the onions:

   • In another skillet, sauté the sliced onion, garlic, and ginger in 1/2 cup of water (or a tablespoon or two of olive oil if you prefer to use oil) on low heat until the onions are soft and lightly golden, stirring frequently to prevent burning and adding a tablespoon or more of water or oil if needed. 

3. Mix it together:

   • Add the cooked onion mix into the broth.

   • Stir in the tamari sauce and mirin.

   • Simmer everything on low for another 10 minutes.

   • Taste and add salt if needed.

     Strain the soup so it is clear.

4. Serve and enjoy:

   • The soup is usually strained to be very clear, but you can leave the onions in for more texture.

   • Top with chopped green onions and some extra sautéed baby portobello mushrooms if you like.

      

     My Notes: 

     *** Mirin is a Japanese cooking wine

     *** Although miso will cloud the soup, you could add it at the end for additional flavor. 

     *** Tamari sauce is mostly gluten-free ( but always read the label to be sure)

     *** My husband likes to add a drop of toasted sesame oil to his bowl.