3 large white onions, sliced 1/4-inch thick
1/2 cup butter, room temperature 1 small shallot, minced
1 teaspoon white truffle oil
2 (14 ounce) Black Angus ribeye steaks
kosher salt and freshly ground black pepper to taste
Preheat oven to 350 degrees F (175 degrees C). Heat 2 tablespoons oil in a saucepan over medium-high heat. Add onions; cook, stirring occasionally, until onions are dark and soft, about 25 minutes. Mix butter, shallot, and truffle oil in a bowl until blended. Refrigerate until set, about 10 minutes. Preheat an oven-safe skillet over medium-high heat. Pour in remaining 2 tablespoons oil. Season steaks with salt and pepper on both sides. Cook steaks until browned, about 2 minutes per side. Cover with aluminum foil. Transfer skillet to the preheated oven and bake until steaks are reddish-pink and juicy in the center, 4 to 6 minutes. An instant-read thermometer inserted into the center should read 130 degrees F (54 degrees C). Let rest in the skillet, covered, about 5 minutes. Slice steaks and transfer to serving plates. Cover with onions; top with a slice of truffle butter.