I have found the best way is get oven to 500 and cook it at 5 min. per pound, then turn oven off and leave it in there for 2 hours, comes out prefect every time. Of course spice to yer liking before cooking. have done 4 or 5 of different sizes over the years and it always works. Only draw back is sometimes the kitchen gets a little smokie.
I usually cris-cross score the fat then season the roast. If time permits, I’ll wrap it in plastic wrap and let it sit for a while. I will then remove the wrap and put the roast under the broiler until I get a good dark (not black) crust, then cook at 300-350 til the meat thermometer hits 120-125. I turn off the oven and partially open the door to torture anyone who is in the house