Preheat the oven to 375°F. Turn each lobster tail over and cut a line down the length of the shell with kitchen shears. Work a finger between the meat and cartilage and gently pull the meat out, keeping it whole.
Brush the lobster meat on all sides with melted butter and bake at 375°F for 12-15 minutes, until it reaches 140°F. Chop into large bite-sized chunks.
Meanwhile, cook the macaroni al dente and drain. Grate the Gruyere, cheddar, and Parmesan.
In a small saucepan, heat the milk until hot but not boiling.
In a large Dutch oven, melt the butter and whisk in the flour. Cook over low heat for about 2 minutes, whisking constantly. Still whisking, add the hot milk and cook until thickened and smooth.
Turn off the heat and add the three cheeses, kosher salt, pepper, and nutmeg. As the cheese melts, stir in the noodles and lobster chunks.
Pour into a casserole dish (or individual ramekins) and sprinkle with the bread crumbs. Bake at 375°F for 25-30 minutes, until bubbling and the top is crispy. Top with chopped bacon for a fancy touch.
