Cauliflower is, in my opinion, a highly underappreciated vegetable. Roasting brings out the natural sweetness of its flavor. Lots of Gruyère and prosciutto add taste and texture.
Technique tip: Always cut cauliflower from the stem end, not the top. You'll keep the florets intact and avoid getting cauliflower crumbles all over your counter.
Preheat the oven to 400°F.2.
Turn the cauliflower upside down on a cutting board. Cut off and discard most but not all of the stems, then cut the florets into small, 1/2-inch clusters. Place the florets on a sheet pan, toss them with the olive oil, red pepper flakes, 1 teaspoon salt and 1/2 teaspoon black pepper, and spread them out in a single layer. Roast for 25-30 minutes, tossing two or three times, until the florets are tender and randomly browned. Set aside to cool for 10 minutes.3.
Set the oven to broil and arrange a rack 6 inches below the heat.4.
Transfer the florets to a large mixing bowl and add the mascarpone, stirring to coat the florets evenly. Stir in the Gruyère, prosciutto, nutmeg, 1 teaspoon salt and 1/2 teaspoon black pepper.5.
Toast the bread in a toaster until lightly browned, and place in a single layer on a sheet pan lined with foil. Mound the cauliflower mixture evenly on each toast and dust with paprika. Broil the toasts for 2-4 minutes, until browned and bubbling (watch them carefully!). Transfer to plates and sprinkle with Parmesan, the chives, and sea salt. Serve hot.