Preheat oven to 350F/180C.
Place tomatoes in a bowl and drizzle with olive oil (I used about 2 tablespoons). Spread the tomatoes out on a baking sheet and sprinkle with desired amount of salt & pepper. Roast for approximately 20 minutes, turning halfway though. Tomatoes should be nicely blistered. Set aside.
Next, separate the cauliflower into bite-sized florets. Blanch in a large pot of boiling water for 5 minutes; drain well.
Lightly grease a 3 qt/3L baking dish. Place the cauliflower and tomatoes in the dish, distributing each well. Tear prosciutto into large pieces and tuck it between, the cauliflower and tomatoes, again distributing it well.
Next, in a small saucepan, melt the butter then stir in the cream and bring it to a simmer and cook for 10 minutes, stirring occasionally. Add 1 1/4 cups of the cheese and simmer for another minute. Add any salt & pepper to taste.
Pour the sauce evenly over the cauliflower mixture, then top with the remaining cheese.
Bake for 30-40 minutes until the top is golden and prosciutto is crispy.