Pull the tenderloin with kitchen twine so that the tenderloin holds its shape. Season the meat with salt, (about 1 teaspoon) let stand at room temperature for about 1 hour, cover with plastic wrap.
Preheat oven 300 degrees. After the meat is soaked, wipe it with a paper towel and brush with melted butter. Cover the baking sheet with foil, put a wire rack on top (as shown in the photo), place the meat on top of the wire rack. Bake in a preheated oven for 55-70 minutes, turning occasionally. The main thing is not to overdry the meat.
While the meat is in the oven, prepare the flavored oil. Put butter in a bowl, add dill, parsley, onion to it and squeeze out the garlic. Season with salt and pepper. Mix everything well.
We wrap the resulting oil in plastic wrap with a sausage, as shown in the photo and place it in the refrigerator. It can also be stored in the freezer for several months.
In a large skillet over medium heat, melt 1 tablespoon of butter. Spread the beef tenderloin and fry for 1-2 minutes on each side (4-8 minutes in total), until each side has a golden crust.
Cut the butter and spread it over the fried tenderloin (as shown in the photo). Let the dish stand for 15 minutes.