Cook the Pasta: First, bring a large pot of salted water to a rolling boil. Add the elbow macaroni and cook it for 1-2 minutes less than the package directions state. We want it al dente because it will continue cooking in the oven. Drain the pasta and set it aside. Do not rinse it; the starch helps the sauce cling.
Make the Roux: Next, using the same pot (less cleanup!), melt the butter over medium heat. Once it's foaming, whisk in the flour. Cook this roux for about one minute, whisking constantly, until it's bubbly and smells a bit nutty. This step cooks out the raw flour taste.
Create the Sauce Base: Gradually pour in the milk and cream, whisking constantly to prevent any lumps from forming. Continue to cook and whisk until the sauce thickens and can coat the back of a spoon. This should take about 5-7 minutes.
Cheese, Please! Now, turn the heat down to low. Add the softened cream cheese, Dijon mustard, garlic powder, paprika, salt, and pepper. Whisk until the cream cheese is fully melted and incorporated. Then, gradually add the shredded cheddar and Monterey Jack cheeses, stirring until you have a perfectly smooth, velvety cheese sauce.
Combine Pasta and Sauce: Add the drained pasta back into the pot with the glorious cheese sauce. Stir everything together until every single piece of macaroni is coated in that creamy, cheesy goodness. This is the heart of your Monster Mac and Cheese.
Prepare for Baking: Preheat your oven to 375°F (190°C). Transfer the macaroni and cheese mixture to a 9x13 inch baking dish, spreading it out into an even layer.
Add the Topping & Bake: In a small bowl, toss the Panko breadcrumbs with a tablespoon of melted butter. Sprinkle this mixture evenly over the top of the mac and cheese. Bake for 20-25 minutes, or until the topping is golden brown and the sauce is bubbly around the edges.
Rest and Serve: Finally, let your magnificent Monster Mac and Cheese rest for about 5-10 minutes before serving. This allows the sauce to set slightly, making it easier to scoop and serve.