Preheat the oven to 400°F and prepare a baking sheet with two long pieces of foil positioned to wrap each tenderloin separately.
Dissolve salt in warm water in a large bag or bowl, then whisk in vinegar, brown sugar, and ice before adding the pork and letting it brine briefly.
Remove the pork from the brine, rinse it thoroughly, and pat it completely dry so the seasoning adheres properly.
Mix the spice blend in a small bowl and rub it evenly over the entire surface of both tenderloins.
Heat oil in a skillet over medium-high heat and sear the pork on all sides until a golden crust forms, then transfer it onto the prepared foil.
Sprinkle the dried herbs evenly over the pork, drizzle with lemon juice, and top with butter slices before sealing each piece tightly in foil.
Bake until the internal temperature reaches the proper range for juicy pork, checking carefully without overcooking.
Let the pork rest with the foil slightly open before slicing, then serve with the buttery juices from the foil.