Pat the steaks dry with paper towels. Season the steak with salt and ground pepper all over. Heat a large cast-iron pan over medium-high heat, add the vegetable oil and heat through.

Add the steak and cook until the bottom develops a golden-brown crust, about 3 minutes. Flip the steaks, and add the butter to the pan. Continue to cook, basting the steak with the melted butter until the steak is medium rare, about an additional 3 minutes. If using an instant-read thermometer, when you insert it into the thickest part of each steak, it should register 120°F (49ªC).

Transfer the steak to a cutting board and let it rest for 10 minutes before thinly slicing the meat.

Return to medium-high heat. Add the shallot and sauté until the shallot is tender and opaque, about 2 minutes. Add the peppercorns, swirling until fragrant, about an additional minute.

Add the cognac and continue to cook over medium heat, allowing the alcohol to burn off for about a minute, then add the beef stock. Simmer until the mixture has reduced by half, about an additional 4 minutes. Whisk in the cream and continue to cook until the sauce coats the back of a spoon, about an additional 2 minutes.

In a medium mixing bowl toss the arugula in the olive oil and red wine vinegar.

Divide the sliced steaks between the bottom halves of ciabatta bread. Top with spoonfuls of the au poivre pan sauce and pile the arugula salad over the top. Garnish with pickled onions then close the sandwiches. Cut in half and serve immediately.