This lobster macaroni and cheese is an upscale version of an old favorite. If lobster is out of the question, consider an imitation lobster in the casserole, or make it with crabmeat, tuna, or lightly cooked shrimp. A garnish of steamed peas adds flavor and vibrant green color to the casserole. Feel free to use peas and carrots, chopped spinach, or broccoli, or leave the vegetables out altogether. For a cheesier casserole, add an extra cup of shredded cheese or sprinkle extra cheese over the top.