Step 1

Preheat the oven to 400 degrees F.

Step 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 to 30 minutes, tossing two or three times, until the florets are tender and randomly browned. Set aside to cool for 10 minutes.

Step 3

Set the oven to broil and arrange a rack 6 inches below the heat.

Step 4

Transfer the florets to a large mixing bowl and add the mascarpone, stirring to coat the florets evenly. Stir in the Gruyere, prosciutto, nutmeg, 1 teaspoon salt, and 1/2 teaspoon black pepper.

Step 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 to 4 minutes, until browned and bubbling. (Watch them carefully!) Transfer to plates and sprinkle with Parmesan, the chives, and sea salt. Serve hot.