03Meanwhile, 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.