Heat half the oil in an oven safe pan over high heat. Sear the beef until browned. Transfer to a slow cooker.
Heat the remaining oil over medium heat. Cook onion, celery, and carrot, stirring, for 6-7 minutes until soft. Add garlic and rosemary. Cook, stirring, for 2 minutes. Then add to the slow cooker along with wine, tomatoes, vinegar, and beans.
Set the slow cooker on high for 3 - 4 hours or low for 6 - 8 hours.
Cook the cauliflower in a saucepan of boiling water for 7-8 minutes until tender. Drain. Use an immersion blender to blend with milk and horseradish until smooth. Season. (Alternatively, blend with a conventional blender in batches or mash with a potato ricer.)
Divide the mash among serving plates and top with the beef.
Serve with baby spinach and cold sweet tea, over ice if desired.