Place steak in a resealable plastic bag. Whisk together 2 tablespoons olive oil, red wine vinegar, garlic, pepper and salt. Pour marinade over steak. Refrigerate 6 - 8 hours or overnight.

Preheat oven to 400 degrees.

When ready to cook, heat a 12 inch (or one big enough to fit your steak) cast iron skillet over high heat until hot. Place steak in pan and cook two minutes. After two minutes, flip and cook for another two minutes. Use a hot pad to hold the handle and transfer the cast iron skillet to the oven and cook for an additional 3 - 4 minutes for medium rare.

Remove steak from the oven, place on a serving platter to rest.

Heat remaining olive oil and butter in a skillet over medium heat until butter melts. Whisk in dijon mustard and capers. Cook 30 seconds - 1 minute or until capers are warmed through.

Slice steak against the grain and spoon sauce over the top. Serve.