"John missed many steak-and-whiskey nights with his law school buddies in 2020, so this dish is for him." —Rach
Arrange the rack in the middle of the oven; preheat to 500°. Line a large rimmed baking sheet with foil and place it in the oven.
In a large bowl, whisk the Worcestershire, sherry, EVOO, garlic, and rosemary. Toss with the cauliflower; season with salt and pepper. Transfer the cauliflower to the baking sheet, spreading in a single layer. Roast until browned at the edges, 15 to 18 minutes. Flip the cauliflower over, top with the cheese, and bake until the cheese is bubbly, about 5 minutes more.
Heat a large cast-iron skillet over medium-high. Season the steaks with salt and pepper. Lightly coat the pan with the cooking oil. Cook the steaks, turning occasionally, about 10 minutes for medium-rare. Using tongs, pick up the steaks and place them on their sides to brown the edges of the meat. Let the steaks rest while you make the sauce.
Reduce the heat to medium, then add the butter to the skillet. When the butter melts, add the shallots. Cook until softened, about 2 minutes. Off heat, stir in the whiskey. Return the pan to the heat and let cook until the whiskey is mostly evaporated, about 5 minutes. Stir in the broth. Let the broth reduce for a minute. Stir in the cream; cook a minute or 2 more. Off heat, stir in the Dijon.
Transfer the steaks to warm plates; top with some sauce. Sprinkle with the parsley. Serve with the cauliflower and more sauce.