01Place a heavy-bottomed soup pot over medium-high heat. Add the peanut oil, and swirl to coat. When oil is hot, add the onion and cook for 5 minutes, stirring, until softened and lightly browned. Add all the aromatics (ginger, lemon grass, cinnamon, star anise, cloves, coriander, fennel, dry chiles and turmeric) and stir to distribute. Add the sugar and let everything fry lightly, until sugar begins to caramelize, about 2 minutes. Add the soy sauce, fish sauce and broth. Bring to a boil, then reduce heat to a gentle simmer. Cook for 30 minutes. Strain, discarding solids. Season to taste with the salt and a generous amount of pepper. (May be prepared several hours ahead.)
02Soak the rice noodles: Put the rice vermicelli in a large bowl. Cover with boiling water. Stir noodles as they soften. Soak for about 20 minutes until tender. Cool in a colander under running water and drain. Reserve at room temperature.
03To serve, bring soup to a brisk simmer. Add the mussels and put on the lid. Cook 2 minutes, until mussels have opened. Add the squid, stir to combine and cook 30 seconds more. Turn off heat.
04Divide rice noodles among 4 large soup bowls. Ladle soup into bowls. Sprinkle with the cilantro, scallions and Thai basil. Pass the fresh chiles and lime wedges separately.