This is from Ina Garten with a few changes. She says to roast 20 minutes for rare, but I thought it was too rare. So, i've added 5 minutes. For a party, leave the roast wrapped up and refrigerate before slicing thinly.
Salt, pepper, garlic powder
Remove meat from fridge at least 2 hours before roasting.
Tie up the tenderloin folding the thin end under itself. Try to make the entire piece of meat about the same thickness, rub all over with oil and season heavily with salt, pepper, and garlic powder.
Preheat oven to 500
Roast 25 minutes for very rare (the thickest part will be very rare, the thinner parts rare); roast 30 minutes for rare.