Melt the butter in a large pot over medium heat. Add the chopped onion and cook for 3 minutes until it softens.
Stir in the minced garlic and cook for 1 minute until fragrant.
Add the chicken pieces to the pot. Sprinkle with salt, pepper, and paprika, then cook for 5 to 6 minutes until the chicken is no longer pink on the outside.
Pour in the tomato sauce and heavy cream. Stir everything together until the sauce looks smooth and evenly mixed.
Reduce the heat to low, cover the pot, and simmer for 15 minutes until the chicken is cooked through and the sauce has thickened slightly.
Remove the pot from the heat. Serve the butter chicken with warmed naan bread on the side.