Ingredients

• 1/3 cup coarsely chopped peeled fresh ginger
• 4 garlic cloves, thinly sliced
• 3 tablespoons water
• 3 kaffir lime leaves
• 1 fresh lemongrass stalk, tough outer leaves removed, 4 inches of thick end thinly sliced
• 1/2 to 1 small whole dried red chile (such as chile de árbol)
• 3 tablespoons peanut oil, divided
• 24 large uncooked shrimp, peeled, deveined, cut in half lengthwise, shells reserved
• 1 large red onion, halved through core, thinly sliced, divided
• 2 tablespoons fish sauce (such as nam pla or nuoc nam)
• 1 rounded tablespoon chopped palm sugar or dark brown sugar
• 4 cups canned unsweetened coconut milk
• 2 1/2 cups vegetable broth
• 10 ounces shiitake mushrooms, stemmed, stems reserved, caps sliced
• 9 ounces dried flat rice noodles
• 4 garlic cloves, thinly sliced
• 1 tablespoon toasted sesame oil (such as Asian)
• 1/2 cup skinless peanuts, toasted, coarsely chopped
• 1/4 cup fresh lime juice
• 1/2 cup thinly sliced green onions
• 1/3 cup fresh cilantro leaves
• 1 lime, cut into 6 wedges

Instructions

1. Place all ingredients in blender. Process until paste forms. Can be made 1 day ahead. Transfer to small bowl, cover, and chill.
2. For soup: Heat 2 tablespoons peanut oil in large pot over medium-high heat. Add shrimp shells and cook until pink, stirring often, about 3 minutes. Add spice paste and half of onion; sauté until dry, about 3 minutes. Add fish sauce and sugar; stir until liquid is syrupy, about 2 minutes. Add coconut milk, broth, and mushroom stems. Bring just to boil, then reduce to medium-low, cover, and simmer 30 minutes. Strain soup into large pot, pressing on solids in strainer. Discard solids. Meanwhile, place rice noodles in large heat-resistant bowl. Pour simmering water over to cover noodles; let stand at least 20 minutes to soften, stirring occasionally (noodles can stand in water up to 2 hours). Heat remaining 1 tablespoon peanut oil in large nonstick skillet over medium heat. Add remaining onion and garlic; sauté until brown, stirring frequently, about 13 minutes. Add sesame oil, then sliced mushroom caps. Sauté until mushrooms are soft, about 4 minutes. Bring soup to simmer. Add mushroom mixture, shrimp, peanuts, and lime juice to soup. Simmer until shrimp is opaque, about 2 minutes. Drain noodles; divide among 6 bowls. Ladle soup over noodles, dividing equally. Sprinkle soup with green onions and cilantro. Serve with lime wedges.
3. Heat 2 tablespoons peanut oil in large pot over medium-high heat. Add shrimp shells and cook until pink, stirring often, about 3 minutes. Add spice paste and half of onion; sauté until dry, about 3 minutes. Add fish sauce and sugar; stir until liquid is syrupy, about 2 minutes. Add coconut milk, broth, and mushroom stems. Bring just to boil, then reduce to medium-low, cover, and simmer 30 minutes. Strain soup into large pot, pressing on solids in strainer. Discard solids.
4. Meanwhile, place rice noodles in large heat-resistant bowl. Pour simmering water over to cover noodles; let stand at least 20 minutes to soften, stirring occasionally (noodles can stand in water up to 2 hours).
5. Heat remaining 1 tablespoon peanut oil in large nonstick skillet over medium heat. Add remaining onion and garlic; sauté until brown, stirring frequently, about 13 minutes. Add sesame oil, then sliced mushroom caps. Sauté until mushrooms are soft, about 4 minutes. Bring soup to simmer. Add mushroom mixture, shrimp, peanuts, and lime juice to soup. Simmer until shrimp is opaque, about 2 minutes.
6. Drain noodles; divide among 6 bowls. Ladle soup over noodles, dividing equally. Sprinkle soup with green onions and cilantro. Serve with lime wedges.