1. Preheat the oven to 425°F.
2. Cook the macaroni according to package directions.
3. Place the flour, milk and nutmeg in the bowl fitted with the whisk. Season with salt and pepper. Mix at speed 7 for 1 minute. Add butter and launch the sauce program at speed 4 at 190°F for 8 minutes.
4. Seed and dice the tomatoes. At the end of the program, add the cheddar and mix at speed 6 for 50 seconds. Add the tomatoes and mix for another 30 seconds.
5. Mix together the macaroni and sauce. Spoon mixture in a 2 1/2 to 3-quart baking dish and sprinkle with the breadcrumbs. Bake for 20-25 minutes. Serve warm.