Directions:

• Preheat broiler to high with a rack about 5 inches from heat source. Place ginger and 1 onion half, cut-sides up, on a large rimmed baking sheet. Broil until charred, about 5 minutes. Transfer to a large saucepan. Add broth, star anise and cinnamon stick; bring to a boil over high heat. Reduce heat to maintain a simmer; cook, stirring occasionally, until reduced to 4 cups, about 20 minutes.
• Meanwhile, drizzle another large baking sheet with canola oil. Bring a large pot of water to a boil over high heat. Add rice noodles; cook according to package directions, about 4 minutes. Drain the noodles and lay them flat on the prepared baking sheet. Set aside. Thinly slice the remaining onion half; set aside.
• Once the broth has reduced, remove and discard the onion half, ginger, star anise and cinnamon stick. Return the broth to a boil over medium-high heat. Stir in bok choy, carrots and mushrooms. Reduce heat to maintain a simmer; cook, stirring occasionally, until the vegetables are tender, about 10 minutes. Stir in shrimp. Cook, stirring once or twice, until the shrimp are opaque, 1 to 2 minutes. Remove from heat. Stir in lime juice, fish sauce and sugar. Divide the noodles among 4 bowls and ladle the soup evenly into the bowls. Serve with the reserved thinly sliced sweet onion, bean sprouts and mint.