Start by making the flank steak marinade. Combine extra virgin olive oil, black vinegar, soy sauce, garlic and peppercorns. Whisk together.

Place flank steak in a resealable plastic bag, pour marinade over the top. Turn to coat. Place in refrigerator and marinade for at least 8 hours or overnight.

Preheat oven to 450 degrees. Place cast iron skillet in the oven for 10 minutes.

While oven and pan are preheating. Combine cilantro, garlic, black vinegar, lime juice, chili pepper and soy sauce in a food processor. Process until chopped fine. With the food processor running, slowly drizzle in the extra virgin olive oil until mixture is smooth. Season to taste with salt. Set aside, at room temperature, until ready to use.

Once skillet is hot, use an oven mitt to carefully remove the skillet from the oven. Place on stove and turn on burner to medium-high heat.

Remove steak from marinade and let excess drip off.

Place steak in heated skillet and cook for 2 minutes per side. Transfer to preheated oven and cook for an additional 5 - 6 minutes for medium rare. Remove from oven, transfer to a plate and loosely cover with foil. Allow to rest for 10 minutes.

Slice steak against the grain and drizzle with chimichurri