Sprinkle the pork tenderloin with the salt and pepper and slice into 8 equal sized medallions.
Melt a generous amount of ghee in a heavy skillet (preferably cast iron) set over medium-high heat. When the pan is hot enough, add the pork medallions and cook them for 4 minutes per side, without moving them, until they develop a nice golden crust. Remove to a plate to collect the juices.
Add the mushrooms to the skillet and cook them, stirring often, until they turn a beautiful golden color, about 5 minutes. Don’t hesitate to add more ghee if and as necessary.
When the mushrooms are cooked to your liking, add the fresh herbs and chicken stock, followed with tapioca starch diluted in water; bring to the boil and continue cooking until the sauce thickens, about 1 minute.
Add the medallions, along with their cooking juices, back into the pan and spoon some sauce over them.
Kill the heat and allow the meat to sit in the sauce for about 5 minutes, then serve.