In a small bowl, soak the prunes in bourbon 1 hour. Preheat the oven to 450 degrees. Drain the prunes, and set four of them aside along with the soaking liquid.

To stuff the roast: Use a sharp knife to cut a 1-inch pocket along the entire length of the eye, around the top half the roast, like forming a tunnel. Cut from both sides of the roast until you cut through.

Stuff three quarters of the soaked prunes into the slit in the roast, and tie the roast securely with kitchen twine at 2-inch intervals. Thread the sage leaves underneath the ties on either side of the roast. Season the roast generously with salt and pepper, and rub it with the olive oil.

Put the roast in a large roasting pan, and roast 15 minutes. Reduce the oven temperature to 400 degrees. Tilt the roasting pan, and spoon off excess fat. Scatter the carrot, celery, onion, and garlic around the roast. Roast an additional 15 minutes. Add the reserved prunes and soaking liquid, and roast 10 minutes. Pour the stock into the pan, and continue cooking, basting the roast occasionally with the pan juices, until a meat thermometer inserted into the thickest part of the roast registers 145 degrees, about 30 minutes more.

Remove the roast to a platter. Pass the contents of the pan through a food mill fitted with the fine disk into a small bowl. (Alternatively, strain the liquid through a sieve, pressing on the vegetables to extract as much liquid as possible and to force some of the vegetables through the sieve). Skim all fat from the surface of the sauce. The sauce should be thick enough to coat a spoon lightly. If not, transfer it to a small saucepan and reduce a bit more. Season the sauce with salt and pepper, if needed. Cut the meat into ¼-inch slices, and serve it with the sauce.