Begin by heating a large 8-quart stock pot over medium-high heat. Add 2 tablespoons of sesame oil, allowing it to shimmer slightly.

Add chopped sweet onion, minced garlic, sliced carrots, and grated fresh ginger to the pot. Sauté for about 5–7 minutes until fragrant.

Pour in 4 cups of chicken broth, 2 cups of beef broth, and 4 cups of water. Raise heat to high and bring to a rolling boil.

Reduce heat to medium-low and let it simmer gently for at least 1 hour.

Carefully remove the pot from heat and extract the vegetables from the broth with a skimmer.

Ladle the warm broth into bowls and garnish with scallions and button mushrooms.