Preheat the oven to 350 degrees F. Use ½ teaspoon of the sea salt to rub over all surfaces of the pork loin and set aside.
Place the cooking fat in the bottom of a heavy, oven-proof skillet on medium heat. When the fat has melted and the pan is hot, add the onions and cook, stirring, about 7 minutes or util just starting to brown. Add the garlic and cook until fragrant, about 30 seconds. Add the mushrooms, remaining salt, and cook another 3 minutes, or until just beginning to soften. Turn off the heat and transfer to a bowl; set aside.
In the same skillet, heat on medium-high, adding some fat if necessary. When the pan is hot, brown the roast, fat-side down, until golden brown, about 5 to 7 minutes. You may want to use tongs to adjust the contact so that the top is evenly browned. Flip the roast so it is fat-side up and add the vegetables back to the pan along with the broth, tarragon, and vinegar. Place in the oven and cook for 40-50 minutes, or until an internal thermometer reads 145 degrees F.
Recipe by Autoimmune Wellness at https://autoimmunewellness.com/mushroom-tarragon-pork-tenderloin/