combine mayo, lemon juice, cajun seasoning, smoked paprika, white truffle oil, lemon juice, black pepper to taste.
Add butter and olive oil to a medium skillet over medium heat. Once the bubble begins to bubble, add in onions and sprinkle with brown sugar. Cook on medium low stirring continuously until soft & golden. Add water as needed. Reduce heat if the onions begin to burn. Once the onions become a deep brown, transfer to a small bowl and set aside.
To make the chimichurri, finely mince parsley, cilantro, garlic and red onion. Add to a medium bowl and combine with red pepper flakes, red wine vinegar and olive oil. Mix well and season with salt and pepper.
Bring steak to room temp before seasoning and cooking. Season with kosher salt and pepper. Press the salt in first, then the pepper. Over high heat, sear steak in a cast iron skillet for 2 minutes on each side. Reduce heat, add butter and aromatics. Baste the steak with the melted butter for 4 minutes. Remove from the pan. Allow steak to rest for 10 minutes before cutting it into thin pieces.
Toast ciabatta bread in the same pan you caramelized the onions.
Remove bread from the pan and spread a creole mustard on one loaf or both. Layer steak and pepper jack cheese. Pop the sandwich in the oven until the cheese is melted. Remove from the oven and set aside.
In a small bowl, toss arugula and Italian dressing together. Layer on the free piece of bread the arugula salad. Add caramelized onions on top of the cheese and then the chimichurri.
Use a knife to close the sandwich. Cut the sandwich in half and enjoy!
