In a large pot, cook the pasta until al dente. Drain the pasta and reserve, also reserve the water. Steam the lobster over the water for 3 minutes, then cool, remove the meat, and reserve both the meat and the shell. In a medium sauce pot, sweat the onions in 2 tablespoons butter, and remove. In the same pot, scald the milk and add the garlic, shallots, and peppercorns. Add the lobster shells to create a fish stock. Bring the "stock" to a boil, then reduce the heat to a simmer, season with salt and pepper, and cook for 20 minutes.
Meanwhile, make a roux by combining 5 tablespoons of flour with 5 tablespoons of butter in a small sauce pot over medium-high heat. Cook until it thickens and develops a golden yellow color. Set aside roux. Strain the stock and return it to the pan. Once the stock begins to simmer again, start whisking the cheeses in slowly until fully incorporated (this will also thicken the sauce). Add the roux to thicken a little more, and then add the reserved onions and lobster meat. Toss the sauce with the pasta, and transfer it to a small baking dish. Top with bread crumbs, and bake for 8 to 12 minutes, or until bubbly and browned.
Different shapes of macaroni make this dish more fun.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.