How to Prepare & cook a ribeye roast beef in the oven
Set the packaged roast on the kitchen counter. Let the roast warm to room temperature for an hour or more. This helps it to cook evenly.
Unwrap and coat the roast with olive or vegetable oil.
Rub with the spices of your choice. Crushed garlic is often used with beef. Some chefs make small incisions in the meat and insert whole cloves of garlic. Other spices commonly used with roast beef include cardamom, thyme, rosemary, sage, kosher salt and pepper. (Use 1 to 2 teaspoons of each.)
Sear the outside of the roast by placing it (fat side up) in a hot oven set to 450 degrees Fahrenheit. After 15 minutes, turn the oven down to 275 degrees and add vegetables like chopped potatoes and onions to the pan. Roasting will take two and a half to three and a half hours at this low temperature but don't cook by time. Use a meat thermometer, preferably the instant read type.
Take the roast's internal temperature after the first two and a half hours. Insert the meat thermometer's spike into the center of the roast making sure that it does not touch any metal. For a rare roast the thermometer should register 135 to 145 degrees. For medium, look for 160 degrees and for well done you'll want to let the roast reach 170 degrees. If it hasn't reached the desired temperature check it every 20 minutes or so. These numbers take into account the fact that the meat will continue to cook for a short while after it's removed from the oven.
When the roast has reached the desired internal temperature remove it from the oven and cover it loosely with aluminum foil. Let it rest for 15 minutes before carving. Slice the roast and place roast and slices onto a serving platter. Garnish with the vegetables.