Heat oven to 425°F
Quarter potatoes and onion, toss on a sheet pan with ghee and salt, and roast 10 minutes
Blend yogurt, cilantro, garlic, ginger, chiles, ghee, garam masala, and salt into a mostly smooth marinade
Coat the chicken with marinade and let sit
After 10 minutes, nestle chicken skin-side up onto the pan, scraping excess marinade over the vegetables
Increase oven to 450°F and roast 30–35 minutes until chicken is cooked and skin is crisp
If needed, roast potatoes longer
Transfer chicken to a plate
Toss vegetables with lemon juice, cream, and hot water, scraping up browned bits to form a sauce
Return chicken to the pan, garnish with cilantro, and serve
