Season the pork fillet with salt and pepper. Fry in hot clarified butter with 1 sprig of thyme all around until golden brown. Then remove the thyme sprig. Put the pork fillet in a non-greased, fire-proof dish and add the second sprig of thyme.
Cook in a warm oven at 90 ° C top / bottom heat for another 70 - 80 minutes. Important: Preheat the oven to 130 ° C and then switch back to 90 ° C. Check with an oven thermo that the temperature remains constant at 90 ° C. The meat is then very tender and roasted pink through and through. It doesn`t need to rest before slicing.
Meanwhile, put the finely chopped shallots in the pan in which the pork tenderloin was seared and sauté with a pinch of sugar. Fry the chanterelles or mushrooms over high heat. Deglaze with a little water, stir in the sour cream and the granulated broth. Briefly reduce until creamy, season with salt and pepper, sprinkle with parsley and serve with the fillet.