Preheat the oven to 375°F (190°C). Line a rimmed baking sheet with parchment paper.
Trim the rinds from the Brie and cut it into small pieces. Add the Parmesan and Alpine cheese to the Brie and mix to combine.
In a medium pot over medium heat, melt the butter. Add the flour and mix it until combined. Cook the mixture, stirring constantly, for 2 to 3 minutes. (This is important to cook off the raw-flour taste.)
Whisk in the milk, mustard, and garlic powder and continue to cook, stirring, until the sauce starts to thicken, 2 to 3 minutes.
Toss in the cheese mixture one handful at a time and stir until completely melted. Season with salt and pepper to taste. (If the sauce is too thick, add milk, 1/4 cup at a time, until the desired consistency is achieved.)
Add the cooked pasta to the pot and toss with the sauce until well coated.
Spoon the pasta mixture into an ovenproof dish, top with the crushed crackers, and bake until the mac and cheese is bubbling and the crust is golden brown, 10 to 15 minutes. Garnish with parsley and serve.