Thai red curry paste imparts simmered-all-day depth to this easy soup that takes less than half an hour to make from start to finish.
In a medium saucepan, whisk curry paste over medium heat until fragrant, 1 minute. Whisk in broth and coconut milk. Add cilantro sprigs, bring to a simmer, and cover. Simmer 10 minutes (do not let boil).
Meanwhile, cook noodles in a large pot of boiling water until just tender, about 2 minutes; drain.
Uncover soup and discard cilantro. Add lime zest and juice, and fish sauce. Add shrimp; simmer until just opaque, 2 to 3 minutes. Stir in noodles; cook 1 minute more. Serve soup topped with cabbage, cilantro leaves, and peanuts, with lime wedges on the side.