Preheat oven to 375°.
Remove the shells from the lobster tails and cut the meat into bite-size pieces.
Melt 2 tablespoons butter in a skillet over medium heat.
Add the lobster meat, season with 1/2 tablespoon Old Bay, and sauté for about 3 minutes, just until cooked. Remove from heat and set aside.
Cook the macaroni in a large pot of salted water for 6 minutes. Drain and set aside.
Crush the Ritz crackers and mix with2 tablespoons melted butter, 1/2 cup grated Parmesan cheese and 2 tablespoons chopped parsley. Set aside.
In a saucepan, melt 1/4 cup butter until slightly browned.
Whisk in 1/4 cup flour and 1 tablespoon Old Bay seasoning, cooking for about 1 minute.
Slowly whisk in 2 cups milk and 1 cup heavy cream, stirring constantly until thickened.
Remove from heat and stir in 2 cups shredded cheddar and 2 cups gruyere until smooth.
Stir in half of the cooked lobster along with any juices from the pan.
Pour half of the cheese sauce into a 9×13-inch baking dish.
Add the cooked macaroni, then pour over the remaining cheese sauce.
Spread everything evenly, then sprinkle the cracker topping over the top.
Scatter the remaining lobster pieces on top.
Bake at 375°F for 20 minutes, until golden and bubbly.