Fill a large pot with water, add a pinch of salt, and bring it to a rolling boil. Add the pasta and cook until just al dente, about 1 minute less than package instructions. Drain and set aside.
In a saucepan over medium heat, melt the butter until it foams and smells nutty, about 1 minute. Whisk in the flour and cook, stirring constantly, until the mixture bubbles and turns a light golden, about 1 minute.
Gradually pour in the warm milk, whisking continuously to create a smooth, velvety sauce. Bring to a gentle simmer and cook until slightly thickened, about 3-4 minutes, with a soft bubbling sound.
Lower the heat to medium-low and stir in the shredded cheddar cheese a handful at a time, waiting for each addition to melt before adding more. Season the sauce with salt and pepper, tasting to balance the flavors. The sauce should be rich, smooth, and cheesy.
Pour the cheese sauce over the cooked pasta and toss gently until evenly coated. Transfer everything to a greased baking dish, spreading it out into an even layer.
Toast the panko breadcrumbs in a dry skillet or oven until golden and crispy. Mix the toasted crumbs with a little melted butter for extra flavor, then sprinkle evenly over the top of the pasta.
Bake in a preheated oven at 375°F (190°C) for 20-25 minutes until bubbling around the edges and the topping is golden brown. For an extra crispy top, broil on high for 2-3 minutes, watching closely.
Remove from the oven and let sit for 5 minutes to settle. Serve hot, with the crispy breadcrumbs providing a delightful crunch against the gooey cheese.
