Preheat oven to 375º Fahrenheit. Combine spices and oil or ghee in a bowl. Place chicken pieces in a large baking dish and coat with oil and spice mixture. Bake for 30 minutes; remove from oven. Preheat broiler then broil chicken for 5 minutes, or until browned in places. Remove from oven and set aside.
In a food processor or high-speed blender, process steamed spinach until puréed. Set aside.
Heat 3 tablespoons ghee in a large skillet over medium-low heat. Add onions, ginger, garlic, and serrano chiles. Cook slowly, stirring regularly, until the mixture becomes a rich medium brown color. Don't skip this part! Add a little water, 1 tablespoon at a time, as needed, if the mixture is burning or drying out.
Add the garam masala, coriander powder, and cumin powder. Sprinkle with a little water to moisten. Cook, stirring frequently, until the spices are fragrant, about 3-5 minutes.
Add the spinach to the skillet and stir well. Add 1 teaspoon salt, half and half, yogurt, and fenugreek leaves. Stir to combine well, then add the chicken and stir gently. Cook about 5 minutes then taste and add more salt as needed.