In a food processor, combine the walnuts, sage, thyme, and garlic. Pulse until the walnuts are coarsely ground.

Spread the walnut mixture and the flour in a large baking pan and mix. Rub the pork tenderloins with 1 tablespoon of oil and season with salt and pepper. Roll the tenderloins in the walnut-herb mixture and gently press the crust mixture onto the pork until it is fully covered.

Cover and refrigerate for at least 1 hour.

Preheat the oven to 350 degrees F.

Add the butter and the remaining oil to a large pan over medium-high heat. When the butter has melted and is sizzling hot, sear the pork, gently turning to to ensure it becomes golden-brown on all sides. Some of the nuts and flour will come off in the pan, which is fine.

Once the pork is seared on all sides, transfer the tenderloins to a baking dish sprayed with non-stick spray. Set the pan aside but do not clean it!

Put the pork in the preheated oven for 20-25 more minutes, or until a meat thermometer registers 155-160°F. Keep in mind, this is for tenderloin. If you make this with pork loin instead, it will take in the neighborhood of 17 minutes per pound, but be sure to check with your meat thermometer occasionally so you don’t over- or under-cook.

Transfer the pork to a plate and tent with foil. Don’t slice quite yet.

As the pork cooks and cools, make your gravy. Take the pan you seared the pork in, and heat over medium heat. There should be some pork juices in the pan from searing. Add the chopped onion to the juices. If there aren’t enough juices to cook the onion, just add in a tablespoon of butter. Sprinkle with 1/2 tablespoon of flour and mix together until thickened and the flour mixture becomes golden, about a minute.

Whisk in the apple cider and chicken broth, a bit at a time, until well-combined and smooth. Season with salt and pepper and add in the bay leaf and apple cider vinegar. Reduce heat to a simmer and cook until reduced and thickened, stirring occasionally. Adjust to taste.

Use a strainer to catch the bay leaf, chopped onion, and any walnuts remaining from the pork while pouring the gravy into a bowl or gravy boat. Discard the solids. Pour the gravy over the pork and serve immediately.