Preheat the oven to 170'C (325'F or Mark 3).
Using a well-scrubbed sharpening steel or some other thick, pointed tool, pierce the beef fillet through the centre, rotate the sharpening steel so as to create a 1 cm (1/2 inch) wide hole.
Combine the thinly sliced basil leaves with the sun-dried tomatoes. Using your fingers, fill the hole with the basil-tomato mixture.
Heat the oil in a heavy, shallow fireproof casserole over high heat. When the oil is hot, sear the fillet until it is well browned on all sides -- 3 to 5 minutes. Transfer the casserole to the oven. For medium-rare meat, roast the beef for 25 to 30 minutes or until a thermometer inserted in the meat registers 60"C (140"F). Remove the fillet from the oven and let it rest until it is cool -- about 45 minutes.