Prepare the Macaroni: Preheat your oven to 350°F (175°C). Boil the macaroni in salted water until al dente, following package instructions. Drain and set aside.

Make the Cheese Sauce: In a large saucepan over medium heat, melt the butter. Add the flour and whisk continuously for about 1 minute until the mixture thickens. Gradually add the milk, whisking constantly to avoid lumps. Let it simmer until it thickens. Stir in the mustard powder, garlic powder, salt, and pepper. Remove from heat and add the cheddar, mozzarella, and gruyere cheeses. Stir until fully melted and the sauce is smooth.

Assemble: Combine the drained macaroni with the cheese sauce, stirring until well coated. Pour the mixture into a greased baking dish. Sprinkle the parmesan cheese evenly over the top.

Bake: Bake in the preheated oven for 25-30 minutes, or until the top is golden brown and bubbly.