Bring a large pot with about 2 liters (8 cups) of water to a rolling boil for the noodles.
While the water heats, prepare the toppings. Slice the spring onions into thin rounds. Roughly chop the watercress. Carefully remove the silken tofu from its packaging, pat dry, and slice into ½-inch (1–1.5 cm) thick pieces.
In a medium saucepan, add 4 cups (1 liter) of water over high heat. Add the kombu dashi powder if using, celery salt, ground ginger, vegetable stock powder, miso paste, sugar, soy sauce, and toasted sesame oil. Whisk until fully dissolved. Bring to a gentle simmer, then reduce heat and keep warm. Do not boil.
Cook the ramen noodles according to package instructions until just al dente. Drain immediately and divide between two bowls.
Stir the broth, then ladle evenly over the noodles. Top with sliced tofu, spring onions, watercress, and a drizzle of la-yu chili oil. Serve immediately.
Video
Notes
Noodles: Use traditional wheat ramen noodles if possible, either fresh or dried. Fresh noodles give the best texture, but good-quality dried ramen works perfectly for this quick version. Avoid instant ramen packets with seasoning sachets.Miso choice: White miso creates a lighter, slightly sweeter broth. Red miso gives a deeper, saltier flavor. Taste and adjust soy sauce as needed.Do not boil the broth: Once the miso is added, keep the broth at a gentle simmer. Boiling can dull the flavor.Salt adjustment: Miso and soy sauce vary in saltiness. Always taste the broth before serving and adjust if needed.Serve immediately: Ramen noodles continue to soften in hot broth. Assemble and serve straight away for the best texture.