There is a reciepe that starts with oven at 500 degrees for 45 min then shuts off oven for 3 hours something like that I have a 12 pound prime ribe to make anyone know? Thanks

No l2 pound piece of meat should be cooked the way you describe. Especially a cut as fine as Prime Rub. Firstly, are you cooing this for a crowd and has it been frozen. If not frozen and not cooking for a crowd I would suggest cutting it into more manageable portions and freezing the rest. This is an expensive cut of meat. The following is a guide on how to cook prime rib:

2 ribs 4 to 5 pounds 450°/325° F 60 to 70 minutes 120° F
3 ribs 7 to 8.5 pounds 450°/325° F 1 1/2 to 1 3/4 hrs 120° F
4 ribs 9 to 10.5 pounds 450°/325° F 1 3/4 to 2 1/4 hrs 120° F
5 ribs 11 to 13.5 pounds 450°/325° F 2 1/4 to 2 3/4 hrs 120° F
6 ribs 14 to 16 pounds 450°/325° F 3 to 3 1/4 hours 120° F
7 ribs 16 to 18.5 pounds 450°/325° F 3 1/4 to 4 hours 120° F

I rub the roast with salt and pepper and flour before cooking. The flour gives a nice flavour and finish to the meat when done and makes that lovely fat portion crackly.

OK thank you I will try this