Caramelise the onions. Melt the butter in a large skillet and add the sliced onions and shallots. Toss to coat the onions in the butter and season with a bit of salt. Cook low and slow, stirring occasionally, until the onions are deeply golden brown.
Season the steak. While the onions cook, liberally season the steaks with salt and pepper on both sides. Drizzle 2 tbs of the Worcestershire sauce over the steaks and really rub the seasoning in. Let the steaks sit at room temperature for at least 30 minutes.
Make the vinaigrette. Combine all the ingredients in a mason jar and blend with an immersion blender. If the dressing is really thick, thin it with a bit of water. Season to taste with salt and pepper.
Cook the steak. Heat 1 tablespoon of a high-heat oil in a cast iron skillet over medium-high heat. Sear the steaks for 4-5 minutes per side depending on thickness. You’re aiming for an internal temperature of 130-140ºF for medium-rare/medium. Alternately, you can grill the steaks on a grill pan or outdoors. Rest the steaks for 10 minutes before slicing.
Assemble the salad. Layer the Florette Mixed in a large bowl or serving platter. Spread the caramelised onions over the salad and top with the sliced radishes, avocado, and chives. Top with the sliced steak and onion vinaigrette and finish with the grated gouda. Serve immediately!
