Peel then slice the ginger into 4 or 5 coins. Smack with the flat side of a knife or meat mallet; set aside. Thinly slice the green parts of the green onion to yield 2 to 3 tablespoons; set aside for garnish. Cut the leftover sections into pinkie-finger lengths, bruise, then add to the ginger.
Coarsely chop the leafy tops of the cilantro to yield 2 tablespoons; set aside for garnish. Set the remaining cilantro sprigs aside. In a 3-to 4-quart (3 to 4 liter) pot, toast the coriander seeds and clove over medium heat until fragrant, 1 to 2 minutes. Add the ginger and green onion sections. Stir for about 30 seconds, until aromatic. Slide the pot off heat, wait 15 seconds or so to briefly cool, then pour in the broth.
Return the pot to the burner, then add the water, cilantro sprigs, chicken, and salt.
Bring to a boil over high heat, then lower the heat to gently simmer for 30 minutes.
While the broth simmers, soak the rice noodles in hot water until pliable and opaque. Drain, rinse, and set aside.
After 5 to 10 minutes of simmering, the chicken should be firm and cooked through (press on it and it should slightly yield). Transfer the chicken to a bowl, flush with cold water to arrest the cooking, then drain. Let cool, then cut or shred into bite-size pieces. Cover loosely to prevent drying.
When the broth is done, pour it through a fine-mesh strainer positioned over a 2-quart (2 liter) pot; line the strainer with muslin for superclear broth. Discard the solids. You should have about 4 cups (1 liter). Season with fish sauce and sugar (or maple syrup), if needed, to create a strong savory-sweet note.
Bring the strained broth to a boil over high heat. Put the noodles in a noodle strainer or mesh sieve and dunk in the hot broth to heat and soften, 5 to 60 seconds. Lift the noodles from the pot and divide between the 2 bowls. Lower the heat to keep the broth hot while you arrange the chicken on top of the noodles and garnish with the chopped green onion, cilantro, and a sprinkling of pepper. Taste and adjust the broth’s saltiness one last time. Return the broth to a boil and ladle into the bowls. Enjoy with any extras, if you like.