how long do you cook a roast beef
1 Put the Roast in the oven and sear for 20 minutes. 2  Then add the water, the chopped onion and reduce the temperature to 275 degrees. 3  Cook for 20 minutes per lb. 4  I like mine rare so that is what you will get if you cook for this period of time. Now Salt and Pepper the rest of the roast. 2  Put the Roast in the oven and sear for 20 minutes. 3  Then add the water, the chopped onion and reduce the temperature to 275 degrees. 4  Cook for 20 minutes per lb. 5  I like mine rare so that is what you will get if you cook for this period of time.