- In stockpot or large saucepan, combine leeks, onion, carrot, celery, mushrooms, lemongrass, ginger, garlic, jalapeños, cilantro stems and 8 cups water.
- Bring to a boil, reduce heat and simmer, uncovered, about 35 minutes.
- Pour stock through a strainer set over a large bowl; discard solids.
- You should have about 5 cups of stock.
- If necessary, add water to measure 5 cups.
- Pour stock back into pot, and reheat if necessary.
- Bring medium saucepan of water to a boil.
- Add rice noodles.
- Let boil 1 minute, turn off heat, and let stand 10 minutes to soften. Drain.
- Remove ¼ cup stock to small bowl; add miso, and stir until dissolved.
- Add miso mixture, noodles, tofu, scallions and watercress to stock.
- Stir in lime juice and cilantro leaves.
- Serve hot with jalapeño rings floating on top.