If I cut roast in half how much does that add to the per pound cooking time? If I start on high temp (450) how long before I turn it down to 250 degrees
?. Then how long at 250 degrees?
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I would personally, go the reverse sear route. Roast low @250 until internal temp 115-120. I'm thinking 2-3 hours for this stage. Pull, tent with foil and set aside while oven comes up to 450+. You can also hold until absolutely ready to complete. Check internal temp before returning to oven. Should be 125+. Monitor. Pull 5-7 degrees below desired final temp. Let sit for 15-20 before slicing. Keep monitoring temp. If you can fit it, I'd keep the piece whole. Using this method, you might find that 130-135 at center is acceptably done. 140 pushing your luck in my opinion. Ends will have plenty of more done meat for anyone skeptical of pink.
It is important to use your meat thermometer in several places. The roast will not cook completely evenly as foodforthought mentions, but that's what you want. An internal temperature range of 125-155 will provide a wide selection of doneness for the diners.
I'd aim for 130 at the center.
I agree to both other answers......you could also cut into two separate roasts. I would also want to add that a good thermometer is crucial. I love my Thermapen. Also see this for great tips..https://food52.com/recipes.... Good Luck!