Slice and season the pork. Cut the pork tenderloin into 1" [2.5cm] thick medallions and pat them dry with a paper towel. Season liberally with salt and pepper on all sides and press the seasoning lightly into the pork.
1 ½ - 2 pounds pork tenderloin, Salt and Pepper
Sear the pork on both sides. Heat oil or ghee in a cast iron skillet over medium high heat. Once the oil is hot and glistening, place the pork medallion in the skillet, flat side down and sear the first side for 2-3 minutes until golden brown. Flip the medallions over to sear the other side for approximately 2 minutes. Avoid over crowding the pan, work in batches if necessary. Remove the pork to a cutting board or cooling rack to rest while you make the sauce.
oil/ghee
Brown the butter. Reduce the heat to medium and add the butter to the skillet. Cook for 2-3 minutes until the butter begins to bubble and brown. Pay close attention to make sure it doesn't burn. You want brown butter not burnt butter. As soon as the butter turns golden brown move on tot he next step.
5 tablespoons butter
Deglaze the skillet. Add the garlic to the butter and sauté for 60 seconds. Add the chicken broth or wine, thyme, and sage to the pan and use a wooden spoon to gently scrape the bottom of the pan to deglaze any pork drippings. Simmer the sauce until the wine reduces and the sauce begins to thicken.
1/2 cup chicken broth or white wine, 2 sprigs fresh thyme, 3 leaves sage, 1 clove garlic
Toss, sauce, and serve. Turn off the heat and add the seared pork medallions to the pan and toss to coat in the sauce. Serve immediately.