Whack lemongrass pieces to crush slightly. Split each piece lengthwise and add to curry mixture, along with remaining coconut milk, broth, ginger, and fish sauce. Bring near to boil; then reduce heat and simmer, covered, for 5 minutes, until flavors infuse. Add bell pepper and snow peas; cook for 3–4 minutes more, until vegetables are just tender. Discard lemongrass and ginger. Stir in lime juice, and season with salt and pepper.