Thai Hot and Sour Shrimp Soup

4 tablespoons vegetable oil
4 cloves garlic, crushed
1 small red onion, finely chopped
7 cups water
1 tablespoon black pepper
1 stalk lemongrass, cut into 2 inch lengths
1 (1 inch) piece fresh galangal root
3 fresh red chilies, thinly sliced
3 fresh green chilies, thinly sliced
4 kaffir lime leaves, scored (if using dry, soak in warm water until pliable)
1 lb medium shrimp, cleaned and deveined
6 tablespoons fish sauce
2 tablespoons fresh lime juice
1/4 cup chopped fresh cilantro

1. Heat oil in a pot with garlic until aromatic; add onion and cook, stirring, until onion is light brown.
2. Add the water and bring to a boil.
3. Add black pepper, lemongrass, galangal, chiles, and lime leaves; return to a boil and boil for 2 minutes.
4. Place shrimp in the pot along with the fish sauce and lime juice.
5. Simmer for 3 more minutes, or until shrimp are firm and cooked.
6. Garnish soup with fresh cilantro before serving.