Cook the pasta: Preheat oven to 400F. Bring a large pot of salted water to a boil. Cook the pasta according to package instructions until al dente.
Cook the bacon: In a skillet over medium heat, cook the bacon until crispy. Transfer to a paper towel-lined plate, then roughly chop into small bits once cooled.
Make the béchamel: In a large saucepan or Dutch oven, melt 4 tablespoons of butter over medium heat. Whisk in the flour and cook for 1–2 minutes, stirring constantly, until the mixture is lightly golden. Slowly pour in the warmed milk, whisking continuously to prevent lumps. Cook for 4–5 minutes until the sauce thickens and coats the back of a spoon.
Add the cheese: Reduce the heat to low and gradually stir in the shredded smoked Gouda and Parmesan cheese until fully melted and smooth. Season with salt, pepper, and garlic powder if using. Avoid boiling the sauce once the cheese has been added.
Add the apples and bacon: Fold the diced Honeycrisp apple and crispy bacon bits into the cheese sauce, stirring until evenly distributed.
Combine with pasta: Add the cooked pasta to the cheese sauce and gently toss until every piece is coated. If the sauce feels too thick, add a splash of reserved pasta water until you reach your desired consistency. Pour into a baking dish.
Toast the Parmesan breadcrumbs: In a small skillet over medium heat, melt 1 tablespoon of butter. Add the panko breadcrumbs and toast for 2–3 minutes, stirring frequently, until golden brown. Remove from the heat and stir in the Parmesan cheese, salt, and pepper.
Finish and serve: Add breadcrumbs overtop the mac and cheese and transfer to the oven. Bake for 10 minutes until browned and bubbly.