Sirloin tip ranks as the most tender cut from the round and doesn't need braising for tenderness, but it can still benefit from a few hours of low-temperature cooking and reverse-searing, or searing after the roast finishes cooking. Choice sirloin tip has a lot of marbling that melts and coats the interior of the meat with unctuous rendered fat and juices as it cooks; low-temperature cooking, to medium-rare to medium, makes the most of it.
You don't have to go beyond salt and pepper when it comes to seasoning, either. Sirloin tip roast has one of the beefiest flavors of all beef cuts – choice gets its flavor from both connective tissue and marbling, the most marbling you'll find next to prime-grade beef. You want to buttress that flavor with as much tenderness as you can, and early salting can help.
Early and heavy seasoning, as in 12 to 24 hours before you want to cook the tip roast, increases tenderness by "loosening" or "unraveling" the coiled muscle fibers that make up beef and helps the salt move deep into the meat.
Save the marinades for cheaper, less beefy cuts like flank or skirt steak. Acidic marinades don't tenderize as well as early salting does, and they alter the pure flavor of a choice sirloin tip roast.
Cooking the Roast
Season the tip roast. Use salt and pepper for the truest beef flavor. If you salted early as well, wipe off the excess salt using a moist paper towel and pat the meat dry.
Heat the oven to the lowest setting. You can set the oven between 200F and 275F, depending on how low your oven goes.
Slow-cook the tip roast for 40 minutes per pound. Cooking time ultimately depends on oven temperature, but you can use 40 minutes per pound as a guide. The internal temperature should measure around 125F for medium rare and 130F for medium.
Sear the tip roast. Heat 1 tablespoon of vegetable oil and 1 tablespoon of butter in a heavy-bottomed skillet over medium (gas stove) or medium-high (electric stove) heat until it starts smoking. Sear the roast on all sides until it turns a rich golden brown color, about 1 minute total.
You can apply this method to any tender cut of meat and get excellent results. Prime rib, tenderloin and strip roasts all benefit from reverse-searing.
To reverse-sear using a grill, cook the sirloin tip roast as usual in the oven. About 30 minutes before the roast finishes, heat the grill to high. Next, sear the tip roast until lightly charred and golden brown, about 1 to 2 minutes total.