1 teaspoon (or up to 1 tablespoon) hot paprika (optional)
1 cup breadcrumbs, toasted
Directions
Preheat broiler. Cook the pasta until just al dente. Drain and Set aside. Meanwhile, toss the cauliflower florets with a little olive oil (just enough to coat evenly). Place in an even layer on a baking sheet and broil, shaking once, until lightly browned (time will depend on your broiler. Mine is junk). Remove and set aside. Lower the heat to 350F.
Melt the butter in a large saucepan over medium-low heat. Add the flour and stir, 2 minutes. Gradually whisk in the cream. Cook until the sauce thickens, whisking occasionally, about 4 minutes. Add about 1½ cups of the Gruyere and whisk until fully melted and sauce is smooth. Whisk in about ½ of the Parmesan, then the creme fraiche and mustard. Add the paprika to taste and season with salt and pepper. Remove from the heat.
Stir together the pasta, cheese sauce, cauliflower, and tomatoes. Spoon in half of the mixture to a large (13x9x2-inch at the minimum) baking dish. Sprinkle with the remaining Gruyere. Cover with the other half of the pasta mixture and top with Parmesan and bread crumbs. Bake pasta uncovered until bubbling, about 35 minutes. Allow to cool a few minutes before serving.
Recipe by Katherine Martinelli at http://www.katherinemartinelli.com/blog/2011/baked-mac-and-cheese-with-cauliflower-and-creme-fraiche/