In a large 8-quart stock pot over medium-high heat, pour 2 tablespoons of sesame oil. Allow it to heat for about 1 minute until it shimmers slightly.

Add 1 chopped sweet onion, 2 minced garlic cloves, 1 diced carrot, and 1 tablespoon of freshly grated ginger. Sauté for about 5-7 minutes, until the onions are translucent and the garlic is fragrant.

Pour in 4 cups of chicken broth, 2 cups of beef broth, and 2 cups of water. Stir gently and bring to a boil over high heat, letting it bubble for 5-10 minutes.

Once boiling, reduce heat to low and let it simmer for at least 1 hour, partially covered.

Use a skimmer or fine-mesh strainer to remove the vegetables, leaving behind the clear liquid. Taste and season with salt as needed.

Ladle the clear soup into bowls while hot, garnishing with chopped scallions and button mushrooms.