Thai Hot and Sour Soup (Tom Yum)

Ingredients
1 ½poundsuncooked medium shrimp
9 ½cupswater, divided
½cupchopped galangal
½cuplemon grass, cut into 1-inch pieces
6kaffir lime leaves
2(15 ounce) canswhole straw mushrooms, drained
2tablespoonsred curry paste (such as Thai Kitchen®)
2tablespoonsfish sauce
2Thai chile peppers, sliced
½cupgreen onions, chopped
½cupfresh cilantro, chopped
2mediumlimes, juiced
Directions
Peel and devein shrimp, reserving shells.
Combine shrimp shells and 6 cups water in a large saucepan; bring to a simmer. Cook for 45 minutes. Add galangal, lemon grass, and lime leaves; simmer 15 minutes more.
Strain broth mixture through a sieve into a bowl; discard solids.
Return broth mixture to the pan. Add remaining 3 1/2 cups water, mushrooms, curry paste, fish sauce, and chiles; bring to a boil. Stir in shrimp, green onions, and cilantro; cook until shrimp are bright pink and firm, about 5 minutes. Stir in fresh lime juice and serve.