For the best, sliceable roast beef, choose an eye of round roast. This recipe will work for anything between 3 1/2 to 4 1/2 lb roast.
Rub the salt over the surface of the beef and wrap tightly in plastic wrap. Store in the refrigerator for at least 12, preferably 24 hours.
Preheat oven to 225F. Dry the surface of the beef with paper towels, then rub with the vegetable oil. Season with pepper. Heat a frying pan with oil until it's very hot, then sear ALL SIDES of the roast. You can hold the ends up with a pair of tongs. It should take about 10 minutes to get a good, hard sear on the meat.
Place the beef on a wire rack, set inside a baking pan - you want it elevated out of any juices.
Roast the meat in the 225F oven for about 1 1/2 hours, then take an internal temperature with a meat thermometer. For medium rare, you'll need 115F; for medium you'll need 125F. Don't go any higher, as this particular cut will be very tough beyond a medium roast.
Once it reaches your desired temperature, turn the oven off, but leave the roast in the oven for another 40 minutes.
Transfer the meat to a cutting board to rest for 10 minutes before carving. Carve very thin slices and serve with horseradish sauce.