Lemongrass and Coconut Curry with Summer Vegetables

Heat oil in a large pot over medium heat. Add 2 Tbsp. curry paste and cook, stirring, until fragrant, about 1 minute. Add white and pale-green parts of scallions, garlic, and ginger. Cook, stirring often and reducing heat if necessary to prevent browning, until softened, about 4 minutes. Increase heat to medium; add vegetables and lemongrass. Cook, stirring occasionally, until vegetables are just beginning to soften, 5–10 minutes. Add broth and coconut milk (add additional broth if needed to cover vegetables) and bring to a simmer. Add chicken, if desired, and basil sprigs; very gently simmer until chicken is cooked through, about 10 minutes. Add 1 Tbsp. fish sauce, if desired. Season to taste with salt or more fish sauce or curry paste for extra flavor and spice, if desired. Garnish with dark-green parts of scallions and basil leaves. Serve with rice and lime wedges for squeezing over, if desired.