Authentic Tom Kha Gai (Thai coconut chicken soup)

Name: Authentic Tom Kha Gai (Thai coconut chicken soup)
Prep time: 15 min
Cook time: 25 min
Total time: 40 min
Cuisine: Thai
Ingredients: 2 cups chicken stock (unsalted, preferably homemade); 1 ½ cups coconut milk; 1 tsp kosher salt (or half the amount of table salt); 1 lb chicken thigh, boneless skinless (bite-sized pieces (see note 1)); 1 stalk lemongrass (bottom half only, smashed and cut into 2-inch pieces); 12 thin slices galangal ((see note 2)); 5 makrut lime leaves (roughly torn into big chunks, center stems removed); 3-4 Thai chilies (bruised or cut into large pieces); 2 Tbsp fish sauce; 1 tsp finely chopped palm sugar, or granulated sugar; 5.5 oz oyster mushrooms; 2 ½ Tbsp lime juice; chopped green onion and/or cilantro, for garnish; Jasmine rice, for serving