Galangal is a rhizome with culinary and medicinal uses, best known for its appearance in Southeast Asian cuisine. It resembles ginger in appearance. However, it tastes little like ginger; in its raw form, it has a soapy, earthy aroma and a pine-like flavor with a faint hint of citrus. It is available as a powder from vendors of Oriental spices and also available in whole, cut or powdered from vendors of herbs.
Lemon grass is widely used as an herb in Asian cooking. It has a citrous flavour and can be dried and powdered, or used fresh. It is usually finely sliced and added to recipes or it may also be bruised and added whole as this releases the aromatic oils from the juice sacs in the stalk.
In my humble opinion, there are no sufficient substitutes for galangal or lemon grass in this recipe.
Measurements are approximate.
1 lb white fish (I used pollock)
2 cups chicken broth
1 can coconut milk
1 tablespoon galangal, julienned
1 tablespoon lemon grass, thinly sliced
¼ cup cilantro leaves, divided
1 jalapeno pepper, thinly sliced
4 tablespoons fish sauce
fresh lime juice from two limes
1 tomato, diced
In a medium saucepan, bring the broth to a simmer. Add the galangal, lemon grass, cilantro, jalapeno, fish sauce and lime juice, and bring back to a simmer.
Meanwhile, heat a large pot on medium high. Add a little olive oil to coat. Add the fish to the pot, and cook for about five minutes per side. Add the broth and the coconut milk to the pot with the fish, and bring back to a gentle simmer, and cook for about five more minutes (or until fish is just cooked).
Garnish soup with additional cilantro and diced tomato if desired.
Information adapted from Wikipedia, recipe from my recipe box.