Buffalo Chicken Mac n Cheese

Preheat the oven to 375 degrees F. Coat a 13- by 9-inch baking dish with cooking spray. Cook pasta according to package directions. While the pasta is cooking, continue with the rest of the dish. Place the cauliflower into a microwave-safe dish, and cook on high 2 minutes. Add the butter to a large saucepan set over medium heat. Once the butter melts, add the onion and celery to the pan. Cook for about four minutes, until the vegetables are soft, then add the garlic. Cook for one minute. Add the cayenne pepper and tomatoes to the pan, stir to combine, then add the flour. Stir constantly for one minute, then slowly pour in the milk while stirring. Drain the pasta. Add the pasta, chicken and buffalo sauce and stir to combine. Pour into the baking dish, then top with the cauliflower and blue cheese. Bake uncovered for 15 minutes, until bubbly. Serve immediately.