Thaw roast in refrigerator for 24-48 hours; remove from packaging, drain excess juice, and pat dry with paper towels.
Preheat oven to 250 degrees Fahrenheit.
Cut rosemary sprig in half and reserve one half for roasting step. Remove leaves from the other half and roughly chop.
Rub roast with whole grain mustard and coarsely chopped rosemary, then sprinkle on Omaha Steaks Private Reserve Seasoning until roast is fully coated.
Preheat a large sauté or roasting pan until very hot, then add cooking oil.
Once oil is hot, carefully add roast and allow to brown on one side. Once browned, carefully rotate with tongs and a spatula on remaining sides until fully browned all over.
Place roast on a wire rack-lined roasting pan, ensuring it does not touch the bottom of the pan, and place the other half of your rosemary sprig on top.
Place in oven and roast for 1 hour and 5 minutes, or until it reaches 130-140 degrees Fahrenheit as per a meat thermometer, for recommended medium-rare doneness; for a different desired doneness, refer to our helpful Roast Cooking Chart. Once the roast has reached your desired doneness, remove from oven and allow to rest for 15-20 minutes before serving.