01 - Preheat oven to 400°F. Generously grease a 2-quart baking dish with butter or cooking spray.
02 - Bring a large pot of salted water to boil. Cook macaroni until just al dente, about 1-2 minutes less than package directions. Drain thoroughly and set aside.
03 - In a large saucepan over medium heat, melt 3 tbsp butter. Whisk in flour and cook, stirring constantly, for 1 minute until fragrant but not browned.
04 - Gradually whisk in milk, about ½ cup at a time, ensuring smooth incorporation after each addition. Cook for 4-5 minutes, stirring constantly, until sauce thickens enough to coat the back of a spoon.
05 - Remove from heat. Stir in cheddar, Gruyère, and Parmesan until completely melted and smooth. Add Dijon mustard, smoked paprika, salt, and pepper, whisking to combine.
06 - Add cooked macaroni and chopped lobster to the cheese sauce. Gently fold until evenly distributed, being careful not to break up lobster pieces.
07 - Pour mixture into prepared baking dish, spreading evenly.
08 - In a small bowl, combine breadcrumbs, melted butter, and parsley. Mix until butter evenly coats all crumbs.
09 - Sprinkle breadcrumb mixture evenly over mac and cheese. Bake for 20-25 minutes until top is golden brown and sauce is bubbling around edges. Let rest 5 minutes before serving.