Boil the pasta. For pasta other than regular durum, cook a minute under box recommendations. Strain pasta and rinse.
Meanwhile, add the ¼ cup flour to a large deep pan. Throw in butter and begin to melt butter and stir until the mixture becomes a paste.
Add in the milk and stock. Stir on a low flame until it begins to thicken and bubble.
Layer in cheese handfuls at a time, stirring to combine and melt cheese, adding more cheese as desired. Season with salt, pepper, and nutmeg.
Add in the cooked pasta and stir to coat. Turn off the flame and keep stirring until the pasta thickens.
Prep an oven safe baking dish, pour in the pasta and sprinkle breadcrumbs.
Bake for 15 minutes and then broil for two minutes or just until top noodles are golden and crisp, and the cheese is slightly browned. Serve immediately.
Notes
Remember to cook the pasta al dente, meaning to the tooth or bite. The pasta will continue to cook when it bakes, so cooking it al dente prevents it from become overcooked and soggy.