Source: Chef Grady Spears, author of The Great Steak Book
1 cup brown sugar, packed
2 tablespoons molasses
2 teaspoons paprika
2 teaspoons dried thyme leaves
1 1/2 teaspoons kosher salt
1 teaspoon garlic powder
To prepare the rub, combine all the ingredients in the bowl of a food processor and process until the mixture is well blended. The rub can be prepared in advance and stored in an airtight container until ready to use.
Using your hands, completely cover the sirloin steaks with the rub, place them on a plate, cover with plastic wrap, and refrigerate for 2 to 4 hours. Remove the steaks from the refrigerator and allow them to return to room temperature while you prepare the grill. Grill the sirloin for 6 to 8 minutes per side for medium rare.