Preheat a skillet over medium heat. Add some oil and saute your mushrooms until the water has evaporated and they are browned (about 8-10 minutes).
Next, add your spinach and cook until it has softened (about 5 minutes). Once done, pull off and let cool.
Carefully butterfly open your beef tenderloin then hammer it until it's a uniform thickness of ½”.
Add your mushrooms and spinach to the beef, then carefully roll it up like a pinwheel. Secure with butcher twine and set to the side.
Soak a 100% white cotton towel in a bowl with all of the red wine for 5 minutes.
Once it's soaked, squeeze out any excess red wine and place the towel flat.
Add 2 cups of kosher salt to the center of the towel and then add 1.5 tbsp of the Bourbon Prime Rub on top of the salt.
Place your beef tenderloin on the salt and then season with the rest of the beef rub.
Add the rest of the salt to the top of the steak so that it is completely encased in the salt.
Roll the towel up to encase the salt covered steak, then secure completely with butcher twine.
Preheat your fire with lump charcoal until the coals are white hot. Blow off any loose ash, then add the steak to the coals to cook for about 20 minutes per side.
Flip the steak halfway through. Once done, pull the steak off and let it rest for 10 minutes.
Once rested, open it up and discard the towel and salt. Brush off any loose salt on the steak. (Optional) If you desire, add the cooked steak back to the grill to get a little crust before serving.
Slice the steak up and top with the Charred Salsa Vinaigrette and enjoy!