Bring water to a light boil in a medium pot. Then place the 2 bags of shredded duck in the pot (without opening them) and cook uncovered for 8 minutes. 4 minutes before they are done cooking, add the red pepper.
Remove the red pepper and the bags from the water. Open the bags with scissors, then empty the meat into a medium bowl lined with a paper towel. Stir the duck meat a little and cover it with another paper towel. Press down on the meat to remove some the excess grease and remove the paper towels from the bowl.
Cut the red pepper into small cubes and add them to the bowl with the duck meat. Set aside.
Cook the pasta al dente in a pot filled with boiling salted water. Drain the pasta and add a few pieces of butter. Mix and set aside.
Preheat the oven on broil. Butter a 2.5-litre (10-cup) baking dish. Set aside.
Preheat a large pot over medium heat and melt the butter. Add the flour, dry mustard and garlic salt and cook for 1 minute, whisking. Add pepper to taste, then add the 15% cream and broth; bring to a boil, whisking constantly.
Remove the pot from the heat. Add three quarters of the cheeses and mix well until they are melted. Add the green onions, the duck meat mixture and the pasta. Reheat for 2 minutes while stirring to completely coat the pasta with the sauce. Adjust seasoning.
Spread the mac n’cheese in the baking dish. Top with the rest of the cheeses. Broil for 5 minutes or until the cheese is golden brown. Serve with a green salad.
