Preheat the oven to 375 degrees.
Grate the blocks of parmesan, mild cheddar, and mozzarella cheeses and place in a large bowl. Mix to combine and set aside. Reserve 1 1/2 cups of the cheese mixture for the roux.
In a medium saucepan, melt 3 tablespoons of butter over medium heat. Whisk in 3 tablespoons of flour.
Slowly add 2 cups of milk to the saucepan, stirring constantly. Add the garlic powder, salt, and pepper and continue stirring until smooth.
Reduce the heat to low and and whisk periodically until sauce has thickened.
Add the reserved 1 1/2 cups of the grated cheese mixture. Stir until melted and smooth.
Remove from heat. Fold in the cooked macaroni pasta until well coated in the cheese sauce.
Next, coat a 9x13 inch baking dish with non-stick spray. Pour the macaroni and cheese sauce mixture into the pan.
Spread the remaining grated cheese mixture over the macaroni. Reserve and set aside 1/4 cup bacon crumbles. Spread the remaining bacon evenly over the cheese.
In a small bowl, melt 1 tablespoon of butter. Add 1/2 cup of Panko bread crumbs and 1/4 cup of the reserved bacon. Stir to combine. Sprinkle the topping evenly over the macaroni and cheese.
Bake for 20 minutes or until golden brown.