Heat two tablespoons of oil in a 12-inch sauté pan that has a lid and at least 2-inch high sides.
2 tbsp neutral oil
Add the shallots and saute them for about 5 minutes, then add the ginger, lemongrass, and Thai chili and saute for another 2 minutes.
3 shallots, 2 tsp grated ginger, 1 red Thai chili pepper, 3 stalks lemongrass (bottom 6 to 8 inches only), bruised with the back of a knife and cut into 2-inch pieces
Add the coconut milk and the fish sauce and bring the liquid to a boil, then reduce the heat to a simmer. Cover the pan with a lid and cook for 20 minutes for the flavors to deepen.
2 cans coconut milk (13.5 oz each), 2 tbsp fish sauce
Add the Thai basil and lime, then taste the broth for seasoning and adjust if necessary. If it needs more seasoning, add more fish sauce or salt.
1 cup Thai Basil leaves, ½ lime, juiced
Gently place the fish filets into the coconut milk, making sure they get covered by the liquid.
1 ½ pounds cod filets (about 4 medium-sized filets)
Bring the liquid up to a simmer and cook for another 7 to 10 minutes, depending on the thickness of the fish, until its internal temperature registers between 130°F and 140°F. Remove the lemongrass stalks and discard them.
Plate the fish on top of a pile of cooked jasmine rice (optional) and spoon some of the coconut broth over it. Garnish with green onions, and chili oil, if using.
Cooked jasmine rice, optional, Sliced green onions, optional, Chili oil, optional