Boil the macaroni in a generous amount of lightly salted water until just tender, about 8 minutes. Meanwhile, preheat the oven to 350°F. Lightly butter an 8-by 8-inch baking dish, or six individual (about 1 1/2 cup) baking dishes and set aside.
Melt the 3 Tbsp. butter in a medium pot set over medium heat. Mix in the flour and cook and stir for 2 minutes. Whisk and dribble in 1/2 cup of milk. Cook until the mixture is quite thick, then slowly whisk in the remaining milk, and then the cream. Bring to a simmer, stirring frequently so it does not scorch on the bottom; cook for 1 minute to thicken and then remove sauce from heat.
Mix in the paprika, cayenne, tarragon, salt and pepper. Now gradually stir in three-quarters of the cheddar cheese until it's just melted and combined with the white sauce.
When the macaroni is cooked, drain it well. Stir the macaroni into the sauce along with the lobster. Spoon the macaroni into the baking dish or dishes. Top with remaining cheddar cheese, and then sprinkle with the Parmesan cheese, panko and parsley. Bake for 25 to 30 minutes, or until light golden and just bubbling.
Note: The milk can be warmed to just below a simmer in the microwave. Cooked lobsters are available in our Seafood Department. You may wish to call ahead to ensure your store has them in stock when you need it. Panko is coarse Japanese-style breadcrumbs sold in our ethnic foods aisle.