Heat a large skillet over medium-high heat.
Add the oil and butter to the hot skillet, then add the diced onion; cook, stirring occasionally, until the onion is lightly golden, about 3–4 minutes.
Add the minced or grated ginger and minced garlic and cook, stirring, for about 30 seconds until fragrant, taking care not to let them burn.
Add the chicken pieces to the skillet, then stir in the tomato paste, garam masala, chili powder (or paprika), fenugreek, cumin, salt, and black pepper until the chicken is coated in the spice-tomato mixture.
Cook the chicken and spice mixture for 5–6 minutes, stirring occasionally, until the chicken is cooked through.
Stir in the heavy cream, reduce the heat to medium-low, and simmer for 8–10 minutes, stirring occasionally, until the sauce is heated through and slightly thickened.
Serve the butter chicken over hot cooked rice with naan on the side.