Baked mac and cheese casserole with a golden, crispy breadcrumb topping over creamy, cheesy pasta is a vegetarian family comfort classic. Rich, indulgent, and crowd-pleasing, it's a holiday table must-have.
Preheat your oven to 375°F (190°C) and butter a 9x13-inch baking dish.
Bring a large pot of salted water to a boil. Add elbow macaroni and cook for 1 minute less than package directions for al dente. Drain and set aside.
In a medium saucepan over medium heat, melt 4 tbsp unsalted butter. Whisk in the flour and cook, stirring constantly, for 1-2 minutes until bubbling but not browned.
Gradually whisk in the whole milk, stirring continuously to prevent lumps. Bring to a simmer and cook until slightly thickened, about 4-5 minutes.
Remove from heat; fold in sharp cheddar and mozzarella cheese until melted. Season with kosher salt, black pepper, mustard powder, and paprika. Taste and adjust seasoning.
Combine cooked macaroni with cheese sauce, mixing well. Pour into prepared baking dish.
For the topping, mix panko breadcrumbs and grated parmesan. Sprinkle evenly over the macaroni mixture.
Bake uncovered for 25-30 minutes, or until the top is golden and crisp and cheese is bubbling. Let rest 5-10 minutes before serving for clean slices.