Special equipment: a flour sack towel; butcher's twine, cut into ten 6-inch lengths
For the chimichurri: Microwave 1 cup water on high for 1 minute. Add the kosher salt and whisk with a fork until dissolved. Refrigerate until slightly chilled, about 20 minutes.
Place the garlic cloves in a blender, then add the oregano and parsley (the garlic should be in the bottom so it meets the blade first). Add the salt water and vinegar and blend on high for a few seconds, just to coarsely chop. Transfer the mixture to a large bowl and whisk in the oil and red pepper flakes. Let sit at least 30 minutes before serving.
For the lomo al trapo: In a bowl, soak a flour sack towel in the red wine until saturated, about 5 minutes. Lightly ring out the towel so it doesn't drip.
Lay out the wine-soaked towel on a clean work surface. Spread the fine kosher salt in an even layer on the towel; it should be about 1/2-inch thick. Press the bay leaves, rosemary, sage and thyme sprigs lightly in the salt, spreading them out to cover all areas of the salt.
Place the tenderloin lengthways on the wide side of the cloth, fold in the ends, like a burrito, and carefully roll the tenderloin in the salt towel. (Don't worry if it's not perfect.) Starting at one end, secure the salted meat roll with butcher's twine, coming around in loops at 4-inch intervals and tying off with a knot.
Prepare a charcoal grill with the grate removed in order to cook the beef directly on the coals. Once the flames have gone out and a bed of charcoal has formed, place the wrapped meat directly on the coals. Cook for 10 minutes on each side, then remove to a cutting board. Allow the tenderloin to rest for 5 minutes before cutting out of the towel. Most often, you will be able to crack the towel like a cast to expose the meat. With a dry pastry brush, brush the salt off the tenderloin. Let rest for another 10 minutes before slicing. Serve with chimichurri.