1. Position a rack in the center of the oven and heat the oven to 250.
2. In a small bowl, combine the olive oil, thyme, garlic, 1 tsp. salt and several generous grinds of black pepper. Put the tenderloin on a heavy-duty rimmed baking sheet or in a small roasting pan and rub the oil mixture all over it.
3. Roast the tenderloin until an instant read thermometer inserted into the thickest part reads 130 for medium rare, about 1 hour. Transfer to a carving board, tent with foil and let rest for at least 20 minutes before serving.
4. Cut the tenderloin crosswise int 1/2-inch slices. Serve with the ragout.