Add the yogurt, lemon juice, turmeric, garam masala and cumin to a large bowl and whisk together. Add the thickly diced chicken and stir to coat. Cover and refrigerate for at least 30 minutes or up to 1 day if you want a richer flavor.
In a large pan over medium heat, melt the ghee (or butter) and add the onions. Cook on medium heat, stirring often, until translucent.
Add the garlic, ginger and cumin seeds and cook for another couple of minutes or until the onions start to brown.
Add the tomatoes, jalapeno pepper and salt and continue cooking for another 10 minutes.
Add the chicken and the yogurt marinade to the pan along with the chicken stock. Bring to a boil, reduce the heat to low and simmer, uncovered, for 30 minutes.
Stir in the cream and tomato paste. Continue simmering for another 15 minutes. Stir in the cilantro (optional) and serve over rice or with naan.