Remove the shells from the shrimp and set aside.
Heat the sesame oil in a large pot set over medium heat. Add the star anise, garlic, and ginger; heat until fragrant, about 30-60 seconds. Pour in the broth, shrimp shells, soy sauce, hoisin sauce, fish sauce, lime juice, and sliced jalapeño. Bring to a boil, then reduce the heat to low and simmer for 20 minutes with the pot covered 3/4 of the way.
While the broth is simmering, cook the noodles according to package instructions. Drain in a strainer, then rinse the noodles with cold water until they are no longer warm to prevent them from continuing to cook. (I also recommend tossing the noodles with a drizzle of oil, like sesame oil, to prevent them from sticking.)
Using a slotted spoon, carefully remove the shrimp shells and discard.
Add the bok choy and shrimp to the broth and cook for 3-4 minutes, until the shrimp are fully cooked and opaque.
Divide the noodles between bowls and ladle the soup over top, garnish and serve hot.