Julienne the carrot, shred the cabbage, thinly slice the mushrooms, and separate the spring onion whites from the greens, slicing both.

Heat the sesame oil in a saucepan, sauté the chopped garlic, ginger, green chili, and spring onion whites for a few seconds until fragrant, then pour in the vegetable stock and bring it to a rolling boil.

Add the carrot, cabbage, mushrooms, and tofu strips to the boiling stock and cook until the vegetables soften slightly but still retain a slight crunch.

Stir in the soy sauce, red chili sauce, rice vinegar, white pepper, and salt, mixing well so the seasoning is evenly distributed through the broth.

Mix the cornstarch with a little water to form a smooth slurry, pour it into the soup while stirring continuously, and simmer until the soup visibly thickens to a glossy consistency.

Reduce the heat slightly and drizzle the lightly beaten egg into the soup in a thin, slow stream while gently stirring in one direction to form delicate ribbons.

Turn off the heat and check the seasoning, adding a touch more vinegar or white pepper if the soup needs a sharper tang or heat.

Let the soup sit off the heat for a couple of minutes so the flavors settle, then ladle it into bowls and garnish with the reserved spring onion greens.