For the Dressing:

1. Heat the butter in a skillet over medium heat. Add in the onion and a pinch of salt and stir to coat in the melted butter. Cook until softened, about 5 minutes.
2. Reduce the heat to low, add in the sugar, and cook for 20 minutes or until the onions are golden brown and super soft. Allow to cool.
3. Add the onions to the bowl of a food processor and pulse a couple times to break them down. Add in the yogurt, buttermilk, and vinegar, along with a pinch of salt and quite a bit of ground pepper. Pulse to combine.
4. Stream in a little more buttermilk if the dressing is too thick. How much you add will depend on the type of yogurt you use.
5. Taste, adjust the seasoning as necessary, and then transfer to an airtight container. The dressing can be made up to a week ahead and kept in the fridge.

For the Steak:

1. Preheat the oven to 350°F and heat a cast-iron skillet over medium-high heat. Pat the surface of the steaks dry with paper towels and then season liberally with salt and pepper.
2. Add about a tablespoon of oil to the hot pan and then add the steaks. Sear over medium-high heat, undisturbed, for about 2 minutes per side. You want a deep, golden brown crust.
3. Transfer the pan to the oven and cook for 5-10 minutes, or until a meat thermometer registers 130°F for medium to medium-rare (actual cooking time will depend on the size of your steaks. I recommend checking after 5 minutes).
4. Remove the steaks from the pan, place on your cutting board, and tent with foil. Allow to rest for 10 minutes before slicing for the salad.

For the Salad:

1. In a large bowl, toss together the greens, onion, avocado, tomatoes, eggs, sliced steak, and dressing. If desired, sprinkle on some bleu or feta cheese crumbles. Serve immediately.