Begin by boiling a large pot of salted water. Add the elbow macaroni and cook according to package instructions until al dente. Drain and set aside.
In a medium saucepan, melt 2 tablespoons of unsalted butter over medium heat. Once melted, whisk in 2 tablespoons of all-purpose flour to create a roux. Cook for 1-2 minutes until it’s lightly golden.
Gradually pour in the 2 cups of whole milk while whisking continuously to avoid lumps. Bring the mixture to a simmer, allowing it to thicken slightly, about 5 minutes.
Remove from heat and stir in the shredded cheddar and Gruyère cheese until melted and smooth. Add in the Dijon mustard, garlic powder, salt, and pepper to taste.
In a large mixing bowl, combine the cooked macaroni with the cheese sauce and the chopped lobster meat. Stir until everything is well combined.
Preheat your oven to 350°F (175°C).
Pour the macaroni and cheese mixture into a baking dish. In a small bowl, mix the breadcrumbs with the 2 tablespoons of melted butter and sprinkle the mixture over the top of the mac and cheese.
Bake in the preheated oven for 20 minutes, or until the top is golden and bubbly.
Remove from the oven and let it cool for a few minutes before serving.