Mix eggs, evaporated milk, 1/2 tsp salt, cayenne pepper and mustard in a measuring cup or bowl.
Boil macaroni in salted water until nearly done. You want to drain when it's al dente, because you're going to continue cooking it on the stove for a few more minutes.
Returned drained macaroni to pot and add the butter to melt and coat the pasta over a low heat.
Add egg mixture and part of the cheese and stir constantly over low heat, about 7 minutes. Gradually add remaining cheese. Season with salt and pepper. (Try a pinch of white pepper if you have it)
If you want to, you can top it with bread crumbs and bake it, but around here, the forks are usually in the pot "testing", before I can get it on the plate.