First Step: Prepare Ingredients Start by chopping the onion finely, mincing garlic if using, slicing the chicken breast into bite-sized or thin strips, and slicing the mushrooms thinly. Peel and slice fresh ginger or galangal, and cut lemongrass stalks into 2-inch pieces, bruising them to release flavor.

Second Step: Build Aromatic Base In a large pot over medium-high heat, combine the chicken stock, coconut milk, ginger or galangal, lemongrass, red curry paste, sugar, and thinly sliced onion. Bring this mixture to a boil, stirring gently to dissolve the curry paste and sugar, then reduce heat to a simmer to develop flavors.

Third Step: Cook Chicken and Mushrooms Add the sliced chicken breast and mushrooms to the simmering broth. Let them cook on medium-low heat until the chicken is fully cooked and firm to the touch, about 4 to 5 minutes. This step ensures the protein is tender and flavors meld with the creamy base.

Fourth Step: Finish the Soup Stir in the fish sauce along with sea salt if desired. Add lime zest (or kaffir lime leaves), fresh lime juice, and basil leaves. Simmer on low until the basil wilts, around 3 minutes. This brings brightness and fresh herbal notes that complement the richness of the soup.

Final Step: Serve and Garnish Remove any large pieces of ginger, lemongrass, or galangal if preferred to make the soup smoother. Serve hot, optionally over cooked jasmine or white rice. Garnish with additional fresh basil, cilantro, sliced green onions, and a drizzle of chili paste or oil for spicy heat if desired.