Step 1: Prepare the Pasta
Preheat your oven to 350°F (175°C). Bring a large pot of salted water to a rolling boil. Add the elbow macaroni and cook according to package directions until al dente (usually 7-8 minutes). You want the pasta slightly firm since it will continue cooking in the oven. Drain well in a colander but do not rinse—the starch helps the sauce cling to the pasta. Set aside.

Step 2: Make the Cheese Sauce Base
In a medium saucepan over medium heat, melt 4 tablespoons of butter. Once melted and foaming, add the flour and whisk continuously for 2-3 minutes to create a roux. The mixture should turn light golden and smell slightly nutty. This cooks out the raw flour taste and creates the thickening base for your sauce.

Step 3: Add the Milk and Cream
Gradually pour in the warmed milk while whisking constantly to prevent lumps. Start with about ½ cup and whisk until smooth, then continue adding the remaining milk in steady streams. Add the heavy cream and continue whisking. Bring the mixture to a gentle simmer, stirring frequently. Cook for 5-7 minutes until the sauce thickens enough to coat the back of a spoon.

Step 4: Incorporate the Cheeses
Reduce heat to low. Add the cream cheese in pieces, stirring until completely melted and smooth. Gradually add the shredded cheddar and Gruyere, one handful at a time, stirring after each addition until fully melted before adding more. This prevents the cheese from clumping. Once all cheese is incorporated, stir in the Dijon mustard, garlic powder, onion powder, paprika, salt, pepper, and cayenne if using. Taste and adjust seasoning as needed.

Step 5: Combine Pasta and Sauce
Add the drained macaroni to the cheese sauce and stir gently but thoroughly to ensure every piece of pasta is coated. The mixture should look very creamy—it will firm up slightly during baking.

Step 6: Transfer to Baking Dish
Pour the mac and cheese mixture into a greased 9×13-inch baking dish, spreading it evenly with a spatula. Gently shake the dish to settle the pasta and remove air pockets.

Step 7: Prepare the Topping
In a small skillet over medium heat, melt 3 tablespoons of butter. Add the panko breadcrumbs and toast for 3-4 minutes, stirring frequently, until golden brown. Remove from heat and stir in the Parmesan cheese, garlic powder, and parsley if using.

Step 8: Top and Bake
Sprinkle the toasted breadcrumb mixture evenly over the macaroni. Cover the dish loosely with aluminum foil and bake for 25 minutes. Remove the foil and continue baking for an additional 15-20 minutes until the top is golden brown and the edges are bubbling. For an extra-crispy top, broil for the last 2-3 minutes, watching carefully to prevent burning.

Step 9: Rest and Serve
Remove from the oven and let the casserole rest for 10 minutes before serving. This allows the sauce to set slightly, making it easier to serve neat portions. Garnish with additional parsley if desired and serve hot.