Preheat your oven to 350°F while you bring a large pot of salted water to a rolling boil. Cook the elbow macaroni for 2 minutes less than the box says—it'll finish cooking in the oven, and nobody enjoys mushy pasta. Drain and set aside, but save 1/4 cup of pasta water just in case you need it later.
In a medium saucepan, melt butter over medium heat, then whisk in flour for exactly 60 seconds without stopping. This is the roux stage, and skipping the whisking means you'll end up with lumps that no amount of straining fixes—I learned this the hard way during my first attempt at baked mac and cheese crowd summer recipe development. You're looking for a light tan color before moving forward.
Slowly pour in whole milk while whisking constantly, then keep stirring for 3-4 minutes until the sauce coats the back of a spoon. The science here: the flour thickens the milk, but only if you keep it moving. If you walk away, a skin forms on top and ruins your texture, so stay present through this step.
Remove from heat and stir in both cheeses plus salt, pepper, and smoked paprika until completely melted. Taste it now—if you want more depth, add another 1/4 teaspoon of paprika because once it's baked, you can't adjust the seasoning. This sauce should taste almost too salty and flavorful on its own; the pasta dilutes it during assembly.
Combine the cooked pasta with shredded chicken in a 9x13 baking dish, then pour the cheese sauce over everything and fold gently 8-10 times. You're aiming for even coverage without crushing the pasta into tiny pieces. If the mixture seems stiff, drizzle that reserved pasta water over the top a tablespoon at a time until it moves freely.
In a small bowl, toss panko breadcrumbs with olive oil, salt, and pepper, then spread across the top of your baked mac and cheese crowd summer in an even layer. Don't pack it down—you want air pockets so it actually browns instead of steaming into a dense brick on top.
Bake for 40-45 minutes until the top turns deep golden and the edges bubble gently around the pan. The filling should jiggle slightly when you shake the dish but not slosh around like soup. Let it rest for 5 minutes before serving—this matters more than people think because the sauce sets just enough to hold the bake together.