Step 1

Cook cauliflower in large pot of boiling salted water until crisp-tender, about 5 minutes. Using large sieve, transfer cauliflower to bowl. Add tomatoes to pot; cook 1 minute. Remove from water; peel and dice tomatoes. Reserve pot of water.

Step 2

Melt 2 tablespoons butter in large skillet over medium-high heat. Add cauliflower; sauté until beginning to brown, about 5 minutes. Add tomatoes and green onions. Cook 1 minute to blend flavors. Remove from heat. Season with coarse salt and pepper.

Step 3

Melt 2 tablespoons butter in large saucepan over medium-low heat. Add flour and stir 2 minutes. Gradually whisk in cream. Cook until sauce thickens, whisking occasionally, about 4 minutes. Add 2 cups Comté cheese; whisk until melted and sauce is smooth. Whisk in 1/2 cup Parmesan, then crème fraîche* and mustard. Season with salt and pepper. Remove from heat.

Step 4

Return reserved pot of water to boil. Add pasta and cook until tender but still firm to bite, stirring occasionally. Drain; return pasta to same pot. Stir in cauliflower mixture and sauce.

Step 5

Butter 13 x 9 x 2-inch glass baking dish. Spoon in half of pasta mixture; sprinkle with 1/2 cup Comté cheese. Top with remaining pasta mixture and 1/2 cup Comté cheese. Melt remaining 1 tablespoon butter in small skillet. Add breadcrumbs and toss to coat. Remove from heat; mix in 1/4 cup Parmesan. Sprinkle crumbs over pasta. DO AHEAD Can be made 2 hours ahead. Let stand at room temperature.

Step 6

Preheat oven to 350°F. Bake pasta uncovered until heated through and bubbling, about 35 minutes.