Trim the brown root ends off the onions but keep the clean part of the root intact.
Quarter the onions lengthwise with their skins on and through the roots so the wedges stay connected.
Trim the stems off the cilantro and tie with kitchen string; save the leaves with tender stems for serving.
Trim and reserve both ends of the jalapeño; thinly slice the remaining chile and save for serving.
In a large pot,over medium heat, toast the star anise, cloves, cinnamon and peppercorns until fragrant; 2 to 3 minutes; transfer to a medium bowl.
Place the onions, ginger and reserved jalapeño ends in the pot; increase the heat to medium-high; char, turning occasionally, until evenly charred; 5 to 7 minutes; transfer to the spice bowl.
Add the chicken, 1 tablespoon salt and 6 cups water to the pot; increase the heat to high; bring to a boil; reduce the heat to maintain a steady simmer; skim off and discard the foam and dirty bits on the surface.
Add the spices and charred vegetables to the pot, along with the sugar, fish sauce and cilantro stems; cover almost all the way and simmer gently, on the lowest heat setting possible, until the chicken is cooked through; about 35 minutes.
Using tongs, transfer the chicken to a sieve and rinse under cold water to help keep the meat from turning gray and to make it cool enough to handle.
Slip the meat off the bones and place the meat in a bowl.
Return the bones and skin to the broth; when it returns to a simmer, taste and add more fish sauce or salt if needed.
The broth should be intensely flavorful, bordering on salty, because the rice noodles will temper its savoriness.
To prepare this dish ahead, strain the broth and refrigerate it and the chicken meat, in separate containers, for up to 5 days.
Bring a large pot of water to a boil; add the noodles and cook until pliable but not soft all the way through; about a minute less than the package directions.
Drain, rinse under cold water until cool; return to the pot.
Add the chicken meat and pour in the broth through a sieve.
Bring to a boil, over high heat; divide among serving bowls.
Top with the bean sprouts, basil and cilantro sprigs and serve with the lime wedges, jalapeño slices, hoisin and Sriracha for seasoning, to taste.