Method

Marinate the Steak

1. In a small bowl, whisk together 3 tablespoons of olive oil, red wine vinegar, sherry vinegar, mustard, and dried thyme. Season the steaks generously with the kosher salt and pepper, rubbing the seasoning into the meat.

2. Place the steaks in a gallon sized zip-top bag, pour the marinade over the steak, and massage it into them, ensuring they’re evenly coated. Seal the bag, getting any excess air out, and let marinate in the fridge for at least 30 minutes, preferably overnight. Prior to cooking, remove from the fridge and allow to come to room temperature on the counter for at least 30 minutes.

Prepare the Onions

1. In a large sauté pan, heat the oil over medium high heat. Once hot but not smoking, add the thinly sliced onions, salt, pepper, and thyme. Cook uncovered, stirring intermittently, for about 10-12 minutes until the onions are golden and soft. Turn the heat to medium-low, add the vinegar, and scrape off any browned bits. Cook the vinegar off of the onions and continue to sauté until the onions get deeply browned, about 5 more minutes. If the pan becomes dry, add water in tablespoon increments.

Cook the Steaks

1. Remove the steaks from the marinade, and let any excess marinade drip off. Heat a cast iron skillet over medium-high heat. Add the remaining tablespoon of olive oil to the pan and swirl to coat. Once the skillet is hot by not smoking, add the pieces of flank steak, leaving space in between them to avoid crowding the pan. You may need to do this in batches, depending on the size of your pan and the steaks. Allow the steaks to get a good, hard sear on one side, 3 to 4 minutes undisturbed before flipping. Cook for an additional 2 to 3 minutes, depending on the thickness of your steak, or until the steaks register 125℉ for medium rare. It will continue to cook while resting. Transfer to a cutting board and allow to rest at least 5 minutes before serving.

2. Slice the steak on the bias, against the grain and drizzle with any juices left in the pan. Season with a pinch of flaky salt, if using.

Assemble the Salad

1. In a large mixing bowl, add the kale, arugula, half of the radishes, and half of the caramelized onions. Add ¼ cup (or desired amount) of SideDish Honey Dijon and using tongs, toss to coat. Transfer the dressed greens to a large serving platter. Top with the sliced steak, remaining radishes, remaining onions, and the gruyere. Serve with extra SideDish Honey Dijon on the side.