Preheat the oven to 350° and lightly grease a deep 9x9 baking dish.
Grate blocks of cheese on large block grater. Set aside.
Melt butter in a large pot over medium heat. Stir in garlic and sauté until fragrant.
Whisk in flour and stir. Once it's combined and looks like paste, start slowly pouring in milk while constantly stirring. Keep whisking until all incorporated.
When the milk is heated through, add cheddar cheese a handful at a time while slowly stirring.
Stir in grated parmesan cheese and season with salt and pepper. Keep slowly stirring.
Once all cheese is melted and smooth, add pasta. Stir until all completely combined. Take off heat.
Spread mac and cheese in the prepared baking dish.
In a small bowl, combine Panko crumbs, grated parmesan cheese, and parsley. Pour in melted butter while stirring until evenly mixed.
Spread topping all over the mac and cheese in the baking pan. Bake for about 20 minutes.