Preheat the oven to 350°F (175°C).
Cook the elbow macaroni in a large pot of salted boiling water until al dente, about 8-10 minutes. Drain and set aside.
In a large skillet, melt the butter over medium heat. Once melted, whisk in the flour and cook for about 1-2 minutes, stirring constantly.
Gradually add the milk while continuing to whisk to prevent lumps. Cook for 5-7 minutes, or until the sauce thickens.
Remove the skillet from heat and stir in the sharp cheddar cheese, Gruyère cheese, Dijon mustard, and season with salt and pepper until fully melted and combined.
Combine the cooked macaroni and lobster meat into the cheese sauce, mixing thoroughly.
Pour the mixture into a 9x13 inch baking dish. If desired, sprinkle breadcrumbs on top for added crunch.
Bake in the preheated oven for 20 minutes, or until the top is golden and bubbly.
Once out of the oven, let it cool slightly. Garnish with fresh parsley before serving.