Melt the ghee or unsalted butter in a large Dutch oven or wide heavy pot over medium heat. Add the onions and Serrano, season with 1 ½ teaspoon kosher salt, and cook, occasionally stirring, until the onions are golden and beginning to caramelize, about 8 to 10 minutes.
Add the ginger and garlic and cook, stirring, until very fragrant and the ginger starts to turn golden and sticks to the bottom of the pot, 2 to 3 minutes. Add the garam masala, cumin, coriander, and paprika, and cook, occasionally stirring, until very fragrant, about 1 minute.
Add the crushed tomatoes and sugar, and bring to a boil. Reduce the heat and simmer uncovered, occasionally stirring, until the sauce has reduced by half and thickens about 30 minutes.
Meanwhile, position a rack directly under the broiler and preheat to high. Line a rimmed baking sheet with foil, set a wire rack inside, and spray the rack with cooking oil.
Arrange the chicken in a single layer on the rack. Broil until the chicken starts to brown in spots, 3 to 6 minutes per side (Don't worry, it will not be cooked).
Remove from the broiler and add the chicken to the simmering sauce; cover and cook until the chicken is cooked through about 10 minutes, or until the desired consistency.
Finish the sauce with heavy cream. Stir, taste, and adjust season with salt and pepper, if needed. Garnish with the chopped cilantro and serve the Chicken Tikka Masala with Cumin Rice and Naan Bread. Enjoy!