Mix the ingredients for marinade together and add meat. Marinate overnight or at least 6 hours
Remove meat from marinade and reserve 1/4 cup. discard the remaining marinade. Let meat come to room temperature about an hour. Dry meat well. Sear the meat in hot pan with some oil on all sides to get a good brown crust. Remove from pan.
mix all ingredients for herb crust together except the panko and butter. Fold up the thinner edges of he tenderloin and secure with butchers twine. Try to get the tenderloin all the same thickness to get a more even bake. Place meat on rack in roasting pan. Spread the crust on the top, sides, and ends of meat leaving the bottom bare. Melt the butter in a saucepan and add the panko and cook until browned. Press the panko on the meat over top the herb mixture.
Place beef in 400 degree oven and roast until internal temp reaches 120 for medium rare, 125 for medium and 130 for well done. Usually between 30 to 45 minutes. Remove the meat from the oven tent with foil and let rest for another 30 minutes
While meat is roasting place oil in large saucepan. cook red onions and garlic until softened. Add the sherry and let most evaporate. Add the broth, bouillon, and herbs bring to a boil. Stir the cornstarch into the reserved marinade and add to Au Jus. Reduce heat and cook until thickened.
Slice the tenderloin and serve with the Au Jus. The Au Jus makes a great tasting gravy also.