Place the topping ingredients in a bowl and stir to combine.
Preheat oven to 400° F.
Cook pasta in salted water* for about 3 minutes less than package directions call for, until al dente, reserving half a cup of the pasta water.
In a large pot melt the butter and then add the flour, whisking continuously over low-medium heat for 2-3 minutes to make a roux.
Slowly whisk in the milk and bring to a boil.
Reduce heat and simmer, whisking occasionally, 3 to 4 minutes, or until sauce is gently bubbling and starting to thicken.
Add reserved pasta water and cheddar cheese and whisk until melted.
Stir in the pasta.
Transfer to a greased 13″ x 9″ baking dish.**
Sprinkle topping on macaroni and cheese.
Bake for 30-40 minutes, or until top is golden and bubbling.
Serve.
* Use about 2 Tbsp of kosher salt for 4 quarts of water.
** If making ahead, mixture can be cooled after this step to room temperature, covered and then refrigerated for up to a day.