Cut up the broccoli and cook using your preferred method. Set aside.
Mix the butter, onion, salt, pepper, and cheese whiz in a bowl until well blended. (If it's kind of stiff you can microwave for a few seconds so it will come together better. Do not melt it, though.) Add the sour cream.
Mix the rice and broccoli into the cheese mixture.
Put in a 9x13 pan and cover with foil. Bake at 325 for 20-25 minutes.