Beef has always been one of the more expensive meats, especially premium-quality cuts, so families for generations have saved dishes like roast beef for special occasions. The centerpiece of traditional "Sunday dinners," roast beef is a rich and hearty comfort food. Prepared right, it doesn't need a lot of extra ingredients, but the trick is to get the beef to the desired level of doneness. Medium rare roast beef is the level between rare and medium. The beef is warm all the way through, but still juicy and red in the middle.
Preheat the oven to 300 degrees Fahrenheit at 30 minutes before cooking. Arrange the oven racks so the middle of the roast will be in the middle of the oven. When you preheat the oven, take the roast beef out of the refrigerator. It should sit at least 30 minutes before cooking.
Trim the fat from the roast. For the most flavorful results, don't trim all the fat. Leave a layer over the top to baste the meat as it cooks. Season the meat as desired.
Place roast beef on a shallow roasting pan, fat side up, in the oven. Do not cover or add liquid. Insert a meat thermometer into the middle of the roast so it touches solid muscle and not fat or gristle.
Estimate how long the beef needs to cook. Cooking time depends on the size of the roast and the cut of meat. Also pay attention to the meat thermometer to ensure the beef is medium rare.
For a standing rib roast or a top sirloin, the meat needs to cook for 20 to 22 minutes per pound. For a top round roast, the meat needs to cook for 30 to 33 minutes per pound. You can also consult a roast cooking chart to determine how long to cook the meat, but these are only estimates. The meat thermometer is the most accurate way to ensure the roast will be medium rare.
Remove roast from oven when the meat thermometer reads 130 to 140 degrees Fahrenheit. The meat should be a deep pink or slightly red in the center, but warmed through.
You can also use the "hand test" to check for doneness. Press the tip of your middle finger to the tip of your thumb, and feel the fleshy base of your thumb. A medium rare roast should have the same feel if you press it with your fingertips.
Let the roast stand 15 to 20 minutes before carving.