Step 1

Using the back of a knife, lightly smash lemongrass and ginger; cut lemongrass into 4” pieces. Bring lemongrass, ginger, lime leaves, and broth to a boil in a large saucepan. Reduce heat and simmer until flavors are melded, 8–10 minutes. Strain broth into clean saucepan; discard solids.

Step 2

Add chicken and return to a boil. Reduce heat, add mushrooms, and simmer, skimming occasionally, until chicken is cooked through and mushrooms are soft, 20–25 minutes. Mix in coconut milk, fish sauce, and sugar.

Step 3

Divide soup among bowls. Serve with chili oil, cilantro, and lime wedges.