These steaks are a great balance between tender and pleasantly chewy, with a great beefy flavor. Top sirloin is best cooked to around medium-rare for best taste and texture.
In a large container big enough to hold the steak, combine the oil, shallots, garlic, and rosemary sprigs with a generous amount of salt and pepper. Add the steak and turn to coat. Marinate, refrigerated for 12 to 24 hours, turning the steak occasionally if possible. Remove the steaks from the marinade and pat dry. Let sit for about 15 minutes at room temperature.
Preheat the grill to medium-high. Carefully oil the grill rack by using grilling tongs to dip a wad of clean paper towels into some vegetable oil, running that over the clean, hot grates.
Season the steak generously with salt and pepper on both sides. Grill the steaks, turning once about halfway through the cooking time for simple grill marks on each side. Or, turn the steaks every two minutes or so, three times in total to achieve cross-hatch grill marks (turn the steaks 90 degrees as you flip them), until the steaks are done to your liking. This should take about 9 to 10 minutes total for rare (120 F internal temperature), 11 to 13 minutes for medium-rare (125 F), and 14 to 16 minutes for medium (130 F).
Remove the steak from the grill to a cutting board. Let sit for 5 to 10 minutes before slicing it across the grain.
Notes
Storage and Leftovers
You can refrigerate an uncooked sirloin steak in its original packaging for up to 4 or 5 days as long as it was freshly cut when you bought it.To freeze sirloin steaks, remove them from the packaging the day you purchase them and wrap them well in plastic. Label a freezer-proof sealable bag with the name of the food (sirloin steaks, of course) and the date you purchased the steaks, and then place the wrapped steaks in the bag. Squeeze out any excess air, then seal the bag and freeze for up to 9 months.Leftover cooked steak should be eaten within 4 days. It can also be frozen using the method above for raw steak, for up to 4 months. Leftover top sirloin steak is great for salads and quesadillas, and sandwiches.