Method:
Preheat the oven to 400°F.
Cook macaroni according to package directions and drain well. Meanwhile, cut peppers into quarters and place in the bowl of a food processor. Add mustard, cayenne, and garlic and process until smooth.
Transfer mixture to a small pot and whisk in milk and flour. Cook over medium high heat, whisking constantly, until thickened. Stir in cooked and drained macaroni and 3/4 cup of the cheese and season with salt and pepper.
Transfer macaroni mixture to a 9x9-inch baking dish. Sprinkle remaining cheese over the top and bake for 20 to 25 minutes, or until browned and bubbly. Serve hot.