Preheat oven to 325 Degrees.
1. Cut small slits into the sirloin tip and place in stainless steel bowl.
2. Combine apple cider, oil, apple cider vinegar, onion, garlic, bay leaf, salt, thyme, oregano, mustard and pepper. Pour over meat. Cover, marinate in refrigerator for 4 hours or more.
3. Remove roast from marinade. Place on roasting pan. Roast at 325 degrees until an instant-read thermometer reaches 140 degrees, about 2 hours for rare meat (meat continues to cook after it is out of the oven). Remove onto warm platter.
4. Strain marinade. Skim fat from roasting pan. Add marinade to the drippings, reserving 2 to 3 tablespoons of the marinade liquid to mix with cornstarch. Stir cornstarch into boiling liquid. Cook until thickened. Glaze roast with the sauce.
5. Slice very thinly to serve.