In a large pot, bring the broth to a boil.
Add the lemongrass, kaffir lime leaves, galangal, garlic and chilies.
Simmer for about 10 minutes to infuse the broth with these flavors.
Add the mushrooms, onions and tomatoes to the pot.
Cook for about 5 minutes until the vegetables are just tender.
Add the shirmp to the pot and cook for about 3-5 minutes or until the shirmp are pink and cooked through.
Remove the pot from heat.
Stir in the lime juice, fish sauce and sugar.
Adjust the seasoning to taste.
Ladle the soup into bowls and garnish with fresh cilantro.
