Bring a pot of salted water to a boil. Cook the macaroni according to package directions, but subtract one minute off of the cooking time since the noodles will cook more in the oven.
Preheat your oven to 350F.
When your noodles are done cooking, drain them and add a tablespoon of butter to them and mix. Set aside. (It's okay if your noodles cool off. In fact, this stops them from soaking in too much liquid while they cook in the oven.)
On medium heat, melt the other one tablespoon of butter in a large saucepan.
When the butter is totally melted, add the flour, whisking constantly.
Once a paste forms, slowly add the milk or cream, stirring constantly.
When your sauce has thickened up but the chunks of flour are mostly mixed in, add your salt, pepper, powdered mustard, and onion powder.
Turn off the heat and add ½ a cup of the cheese, reserving the other ⅓ cup of cheese for the topping. There will still be enough heat in the sauce to melt the cheese.
Once the cheese has melted and the sauce is a good consistency, add your cooked noodles to the sauce pan. Stir until the noodles are coated in the sauce.
Grease an oven-safe dish with butter. Pour your noodles and sauce into the dish. Add the remaining cheese on top.
Bake for 15-20 minutes or until the top is nice and bubbly and just how you like it.
Let sit for a few minutes before you serve it. Top with some dried parsley if you'd like and ENJOY!