Pat the Osso Bucco dry with a paper towel and brush meat with Dijon mustard. In a bowl, combine the flour, salt and pepper. Dredge the Osso Bucco in the seasoned flour.
Place a casserole dish or dutch oven onto medium heat and add oil. Sear Osso Bucco (one piece at a time) on both sides for 2-3 minutes until browned. Transfer to a plate and set aside.
In the same pan, add onion, carrot, celery and cook on medium for 5 minutes until softened. Add garlic, thyme and curry paste and cook for 2 minutes until fragrant. Add in wine and simmer for 2 minutes, scraping the pan to incorporate the fond (brown bits). Stir in broth and tomatoes and bring to simmer.
Place the browned Osso Bucco back into the dish, ensuring the meat is covered by liquid and vegetables. Place the lid on the dish and cook in the oven at 160°C for 2 ½ hours until tender.
To make the cauliflower mash, bring a large saucepan of water to a boil. Add cauliflower and boil for 10 minutes. Drain and stand for 2 minutes so that cauliflower dries off. Melt butter with milk or cream in the sauce pan and add the cauliflower back into the pan. Run through with an immersion blender until smooth. Stir in parmesan and season with salt and black pepper to taste. Serve with Osso Bucco.