Rump roast comes from -- you guessed it -- the back end portion of the steer. Also known as bottom round, rump roast is a fairly tough roast that needs long braising to tenderize it. To make a roast without any seasonings, you need to pay extra attention to the type of roast you buy, how you prepare it and how you cook it. Otherwise, the roast will be tough and flavorless.
Buy the best-quality rump roast you can afford. Roasts labeled "Prime" have more marbling, which means they're naturally juicy and flavorful. "Choice" is the next grade, followed by "Select." Prime roasts are generally found only in specialty stores, but you an easily find Choice or Select grades at the local grocery store.
Unwrap the roast from its packaging. Rinse it and pat it dry with paper towels. Wrap it in clean, white kitchen towels or sheets of cheesecloth. Set it on a rack placed on a baking sheet and store it in the refrigerator at 40 degrees Fahrenheit for up to 5 days. This simple technique dry-ages the roast so it tastes better and has a buttery flavor.
Remove the roast from the refrigerator and remove the cheesecloth or towel. Cut away any dried, hardened areas with a sharp knife. Allow the roast to sit at room temperature for up to 2 hours. Allowing the roast to come to room temperature helps it cook more evenly.
Preheat the oven to 275 degrees Fahrenheit. Pour a bit of vegetable oil in a large oven-proof roasting pan or Dutch oven and heat it over medium heat. Add the roast and brown it on both sides. Browning an unseasoned rump roast before cooking it helps seal in the juices and caramelizes the roast so it has more flavor.
Add enough water to the pan to partially cover the roast, but don't submerge it. Put the lid on the pan and cook the roast for 2 or 3 hours, or until the roast is fork-tender and a meat thermometer registers at least 160 F. The U.S. Department of Agriculture suggests roasts be cooked to at least 145 F, but cooking a rump roast to this higher temperature ensures a more tender texture.
Remove the roast from the pan and set it on a carving board. Cover it with foil and allow it to rest for 10 to 15 minutes before cutting it. This resting period allows the juices to settle and makes carving easier. Serve the roast with the juices from the pan.