Combine the chicken in a bowl and sprinkle with the cumin, coriander and a bit of salt. Chill in freezer for 30 minutes, this will make it easier to grind the chicken up. Place everything in a food processor, along with the lemongrass and pulse until finely ground (do in batches if necessary).
Shape meatballs by the tablespoon (about 16), wetting your hands in cold water if necessary to prevent meat from sticking to your hands. Using a bit of oil, fry meatballs in batches until browned on all sides (about 1 minute per side – will not be fully cooked), then set aside while you make the broth.
In a bit of oil, sauté the shallots, jalapeno and salt until tender. Stir in the chicken broth, coconut milk and bring to a boil. Add the herbs and pulse with an immersion blender a few times if want a smoother sauce. Add the remaining lime juice, sugar and fish sauce to the pot along with the partially cooked meatballs.
Cover and simmer for 20 minutes, or until meatballs are fully cooked (165F). Add the carrots during the last few minutes. For a thicker broth, remove the cover after 10 minutes