Cut the chicken into pieces (if not already cut). Cube the potatoes, chop the onions, mince the garlic, and grate the ginger.
Lightly bruise the lemongrass by hitting it with the back of a knife. This releases its aroma.
Heat 2 tbsp oil in a large pot or Dutch oven over medium-high heat.
Add the chicken pieces and cook for 5-7 minutes, turning occasionally until lightly browned on all sides. Remove the chicken from the pot and set it aside.
In the same pot, add the chopped onions. Sauté for 5-7 minutes until golden brown.
Add the minced garlic, grated ginger, and bruised lemongrass. Cook for 1-2 minutes until fragrant.
Add curry powder, turmeric, cumin, coriander, fennel seeds, cinnamon, and chili powder (if using). Stir well to coat the onions in the spices. Cook for 1-2 minutes.
Add the chopped tomatoes to the pot. Stir and cook for 3-5 minutes until the tomatoes soften and break down.
Pour in the chicken broth and coconut milk. Stir well to combine.
Return the chicken to the pot along with the cubed potatoes. Stir to coat everything in the sauce.
Bring the curry to a boil, then reduce the heat to low. Cover and simmer for 20-25 minutes, stirring occasionally, until the chicken is tender and the potatoes are fully cooked.
Taste the curry and adjust the seasoning, adding more salt if needed.
Remove the bruised lemongrass stalks before serving.
Serve hot with steamed rice, jasmine rice, or roti. Enjoy!