Marinate: Toss chicken with marinade ingredients. Let sit for at least 30 minutes.
Sear: Heat oil in a large pan. Sear chicken on all sides until lightly browned, then transfer to a large stockpot.
Build Base: In the same pan, sauté shallots and garlic. Stir in extra curry powder until fragrant, then add to the stockpot.
Simmer: Pour chicken broth into the pot. Bring to a gentle boil, then lower to a simmer. Add carrots, potatoes, and sweet potatoes in succession, 10 minutes apart. Simmer 40–50 minutes total until chicken is tender.
Finish: Add coconut milk. Taste and adjust with salt, fish sauce, or sugar. Mix corn starch with a cup of broth to create a slurry, then stir it back into the pot to thicken.
Serve: Garnish with cilantro or Thai basil. Serve with a crispy baguette, rice noodles, or steamed rice.