For the Tenderloin: Set out Tenderloin in a zip-lock bag so to be at room temperature when marinade is ready.
Marinade: In a small sauté pan add 2 Tbsp olive oil. Sauté garlic till golden, add 1/2 of the diced onion; sauté till clear.
Turn the heat up a bit and add the sage, marjoram, thyme, ginger and celery seed; sauté till you just smell the spices coming out (about a minute).
Remove from heat. Mix in woy and Worcestershire wauce.
Take tenderloin and add marinade to bag. Force out air and seal.
After about an hour massage the marinade into the meat. Have fun; pound on it with your fist, squeeze it as you wish for about 5 minutes. At 2 hours do it again. It will feel tenderized and will have taken on the color of the spices by now. Don't beat it up so much that it starts to come apart (just close)! While the meat is getting tasty in the bag make the sauce.
For the Sauce: In a sauté pan add 2 Tbsp olive oil. Add the rest of the onion, the mushroom pieces and the salt and pepper. Sauté till onions clear (about 10 minutes).
Stir in apple juice and milk. Reduce to your desired thickness. You can add more milk and juice as you go if you wish. Go Slow so you don't have to keep stirring it too often.
Roasting the Tenderloin: Preheat oven to 350°F.
On Med-High add 2 Tbsp olive oil to a sauté pan. Just when the oil smokes take the tenderloin and sear all sides as quickly as possible till just golden brown.
Remove to a baking dish and roast for 40-45 minutes. Remove from oven and let stand for 10 minutes.
Pour heated sauce over Tenderloin. Slice and serve.