Preheat oven to 375 F. Butter a 13x9-inch baking dish; set aside.
Cook macaroni according to package directions.
Drain, and return to pot.
Add butter, and toss to coat pasta in butter.
In a separate medium bowl, whisk together evaporated milk, half-and-half, and eggs.
Add salt and mustard; set aside.
In another medium bowl, stir together cheeses; set aside.
Place 1/3 macaroni in prepared baking dish.
Top with 1/3 cheese.
Repeat layers with remaining macaroni and cheese.
Pour milk mixture evenly over baking dish.
Cover with foil, and bake for 30-40 minutes, or until hot and cheese is melted.
Remove foil, carefully stir macaroni, and then sprinkle with extra cheese, if desired.
Continue baking, uncovered, for about 10 minutes, or until cheese is melted and macaroni and heated through.
Let stand 10-15 minutes before serving.
*Feel free to top with an additional cup of cheese after stirring. **If you would like to make this casserole ahead of time, increase the amount of evaporated milk by 1 cup. Cover, and refrigerate for up to 24 hours. Set the casserole out while the oven preheats, and then add about 5-10 minutes to the baking time. ***Nutrition values are estimates.