Dinner Tonight: Spiced Shrimp Soup

Name: Dinner Tonight: Spiced Shrimp Soup
Ingredients: 4 stalks fresh lemongrass, tough outer leaves discarded, ends trimmed; 1 pound shrimp, shells removed and set aside; 6 cups water; ¼ cup cilantro roots, well rinsed; ½ teaspoon salt; ½ teaspoon black pepper; 1-inch cube fresh ginger, cut into fine strips; ¼ cup asian fish sauce; ¼ cup fresh lime juice; 1 small red or green thai chili or serrano, stemmed, seeded, and sliced thinly; 2 tablespoons cilantro leaves, chopped; 1 red chili, thinly sliced (optional)