Directions

1. For the cauliflower purée, combine the chopped cauliflower and cream in a small saucepan. The cauliflower should be mostly covered in cream, add a little bit more if needed (don’t add too much or the purée will be thin). Bring the cream to a boil over medium-high heat, then reduce the heat to medium and simmer until the cauliflower is very tender, 12 to 15 minutes. If the cream bubbles up a lot, reduce the heat to medium-low. Add the cheese and stir until melted. Take the pan from the heat and use an immersion blender to purée the cauliflower until smooth. Or, transfer the mixture to a food processor and process until smooth. Season to taste with salt, setting the purée aside in the saucepan until ready to serve.
2. For the demiglace sauce, stir together the beef stock and tomato sauce in a small saucepan. Bring to a boil over medium-high heat, then reduce to medium and boil gently until reduced to about 1/2 cup, 20 to 25 minutes. Set aside in the saucepan until ready to serve.
3. Preheat the oven to 400°F.
4. Heat the oil in a medium skillet over medium heat. Add the blanched potatoes, mushrooms, and onion with a good pinch each of salt and pepper and cook, tossing occasionally. After about 2 minutes, add the garlic. Continue cooking until the potatoes begin to brown, about 2 minutes longer. Add a bit more oil as needed if the pan becomes dry. Use a slotted spoon to add the julienned beet to the skillet, also adding about 1/4 cup of their soaking water. Continue cooking the vegetables, stirring occasionally, until the potato and mushrooms are tender and the liquid has evaporated, 2 to 3 minutes longer. The beet will still have some crunch. Set aside off the heat while cooking the steak.
5. Melt the beef tallow or butter in a large heavy ovenproof skillet over medium-high heat. Season the steaks with salt and pepper, then add them to the hot skillet. Sear the steaks well, about 2 minutes on each side, then put the skillet in the oven and continue cooking the steaks to taste, about 6 to 10 minutes for medium rare (135° internal temperature), depending on their thickness, or to suit your taste. Transfer the steaks to a plate, cover, and let rest for 5 to 10 minutes before serving.
6. While the steaks are resting, reheat the cauliflower purée and demiglace sauce over low heat. Reheat the hash over medium heat. Add the arugula to the hash and toss to mix, then take the skillet from the heat and stir in the blue cheese.
7. To serve, spoon the cauliflower purée on warmed plates, spreading it out evenly. Drizzle the demiglace sauce over, then spoon the hash over the purée. Set the steaks on the hash, topping them with sprouts if using. Serve right away.