Ingredients:

• 2 cloves garlic, sliced
• 1 shallot, sliced
• 1 teaspoon ground chili paste
• 1 fresh red chili, any kind (optional)
• 1 tablespoon chopped fresh cilantro
• 1 teaspoon whole black peppercorns
• 2 tablespoons vegetable oil
• 1/3 pound raw medium shrimp, peeled and deveined (reserve the shells)
• 5 cups chicken stock or chicken broth
• 1 stalk lemon grass, cut into 1-inch pieces and bruised with the back of a knife
• 3 thin slices galanga
• 3 Kaffir lime leaves, cut into thirds
• 3 tablespoons fish sauce
• 1 tablespoon brown sugar
• ½  cup drained canned straw mushrooms or sliced white mushrooms
• 2 red ripe tomatoes, cut into thin wedges
• 1/3 cup fresh lime juice
• 10 fresh basil leaves
• 5 fresh cilantro sprigs, chopped

Directions:
Place the garlic, shallot, chili paste, chili, cilantro, and peppercorns into a mortar and pound into a paste.
Heat the oil in a soup pot over moderate heat. Add the shrimp shells and brown until fragrant, about 2 minutes. Add the spice mixture to the pot and stir until fragrant, about 20 seconds. Add the chicken stock and let simmer for 5 minutes. Using a slotted spoon, remove the shells and discard. Add the lemon grass, galanga, lime leaves, fish sauce, brown sugar, mushrooms, and tomatoes and bring to a boil. Add the shrimp and cook until almost done, about 2 minutes.
Remove from heat and add the lime juice, basil, and cilantro. Serve piping hot.