Pat the 700g chicken thighs dry with paper towel and cut them into large, even pieces of about 4–5cm. In a mixing bowl, combine the 1½ tbsp curry powder, 1 tbsp fish sauce, 1 tsp sugar, ½ tsp turmeric, ½ tsp black pepper and the 2 minced garlic cloves. Add the chicken and mix thoroughly with your hands or a spoon until every piece is evenly coated. The marinade should cling as a genuinely thick, concentrated golden spice coating rather than pool as a watery liquid. Cover and refrigerate for 20–30 minutes. That dry, concentrated coating is what lets the curry powder season the chicken directly and toast properly when it hits the hot pot.

While the chicken marinates, peel the 500g potatoes and cut them into large chunks of about 3–4cm, then cut the 250g carrots into thick rounds of 1.5–2cm. Thinly slice the onion, finely chop the 2 shallots and finely mince the 3 remaining garlic cloves. Trim the 3 lemongrass stalks, peel away the tough outer leaves and bruise the lower portions firmly with the back of a knife, then cut them into 5–6cm sections that will be easy to lift out later. Keep each ingredient in its own pile. That generous potato size is genuinely what lets the chunks survive the simmer without breaking down and releasing so much starch that the curry turns into a heavy potato stew.

While the chicken finishes marinating, heat 1 tbsp neutral oil in a large heavy skillet over medium-high heat until it shimmers. Add the potato chunks in a single layer and cook for 4–6 minutes, turning occasionally, until lightly golden on several surfaces. The centres should still be firm and clearly raw when pierced with a knife; do not aim for crisp, fully fried potatoes. Transfer to a plate and set aside. If the oil starts to smoke, lower the heat slightly rather than letting the edges scorch. That light golden exterior is what develops a gentle roasted flavour and helps each chunk hold its structure through the long simmer ahead.

Heat 2 tbsp neutral oil in a heavy-bottomed pot or Dutch oven over medium-high heat. Add the marinated chicken in a relatively even layer, working in two batches if the pot is crowded, and leave it undisturbed for 2–3 minutes per side, until the outside is lightly golden and smells of toasted curry. The chicken does not need to cook through at this stage. Transfer it to a plate, keeping any juices, and leave the browned spice residue in the pot. If the coating darkens quickly or smells sharp, lower the heat at once. That controlled medium-high heat, rather than maximum heat, is what browns the chicken without scorching the finely ground spices into bitterness.

Reduce the heat to medium. Add the sliced onion and chopped shallots to the same pot and cook for 3–4 minutes, stirring occasionally, until softened and lightly golden. Add the 3 minced garlic cloves and the bruised lemongrass sections and cook for 1 minute, stirring continuously. Sprinkle in the 1 tbsp curry powder and cook for 30–45 seconds, until genuinely fragrant. If the pot looks dry or the spices start to catch, add a small splash of the measured chicken stock and scrape the bottom. Have the chicken and potatoes within reach before any liquid goes in. That short toasting of the aromatics is what cooks out any raw garlic or uncooked curry powder smell before the broth is built.

Pour in about 200ml of the coconut milk, stirring and scraping to release the browned seasoning from the bottom of the pot. Cook gently for 2 minutes, letting the curry powder disperse into the coconut fat. Add the remaining 200ml coconut milk, the rest of the 400ml chicken stock, 1 tbsp fish sauce and 1 tsp sugar, and stir until fully combined. Return the browned chicken and any accumulated juices to the pot and bring to a gentle simmer over medium heat. The broth should turn a warm golden-yellow with a delicate sheen of spiced coconut fat. That first small addition of coconut milk is what blooms the curry powder in fat, so the colour and flavour spread evenly through the whole broth.

Add the lightly fried potatoes and the carrot rounds and stir gently to distribute them among the chicken pieces. Bring back to a gentle simmer, partially cover and cook for 18–25 minutes, stirring carefully once or twice, until the chicken is tender and reaches 74°C / 165°F, the potatoes pierce easily with a knife and the carrots are tender but still hold their shape. The broth should be lightly thickened yet clearly pourable. If it reduces too quickly, add 50–100ml hot water or extra stock. Keep the bubbles small and lazy, never a rolling boil. That gentle, careful simmer is genuinely what keeps the coconut broth smooth and stops softening potatoes breaking apart and clouding the curry.

As soon as the curry goes on to simmer, place the 200g jasmine rice in a fine sieve and rinse under cold water several times, until the water runs mostly clear, then drain thoroughly. Transfer to a small saucepan with the 270ml water and the ¼ tsp salt, if using, and bring to a boil over medium-high heat. Stir once, reduce the heat to the lowest setting, cover tightly and cook undisturbed for 12 minutes. Turn off the heat and leave it covered for another 10 minutes, then fluff gently with a fork. If your rice brand calls for a different water ratio, follow it. That covered rest is what redistributes the moisture and leaves distinct, tender grains with no excess water.

Remove the lid and taste the broth. Add more fish sauce for savoury depth and saltiness, a small pinch of sugar if the spices feel harsh, and salt only if it still needs it. If the broth is too thick, loosen it with a little hot stock or water; if it is too thin, simmer uncovered for a few more minutes. Lift out and discard the lemongrass sections. The curry should taste warmly spiced, gently sweet from the coconut milk, savoury from the fish sauce and aromatic with lemongrass, never aggressively hot. That final tasting is what preserves the curry's loose, broth-like character rather than reducing it into a heavy gravy.

Divide the fluffed jasmine rice evenly among 4 bowls, each holding the cooked equivalent of about 50g uncooked rice, and keep it grouped neatly to one side. Spoon the curry beside the rice, giving each bowl about 175g raw-weight chicken, 125g potatoes, a generous share of carrots and plenty of golden coconut broth surrounding the chicken and vegetables. Scatter over the 15g cilantro leaves and finish with a light dusting of freshly cracked black pepper. Add lime wedges on the side, if using. Serve immediately, while the broth is hot and glossy. That side-by-side arrangement is what lets the rice soak up the broth gradually instead of turning soggy at once.