1 pound elbow macaroni
4 pounds Cheddar cheese, sliced
1 1/2 cups milk
5 eggs, or more to taste
1 tablespoon yellow mustard
ground black pepper to taste
Preheat oven to 300 degrees F (150 degrees C).
Bring a large pot of lightly salted water to a boil. Cook elbow macaroni in the boiling water, stirring occasionally until tender yet firm to the bite, 8 minutes. Drain.
Layer some of the macaroni in a 5-quart baking dish; top with a layer of Cheddar cheese. Continue layering macaroni and Cheddar cheese into the dish, ending with a Cheddar cheese layer.
Beat milk, eggs, and mustard together in a bowl; pour over macaroni mixture, ensuring milk mixture gets to all of the macaroni.
Bake in the preheated oven until cheese is melted and just before cheese around the sides gets crisp, 20 to 25 minutes. Season with black pepper.