Preheat your oven to 350 degrees F (175 degrees C) and grease a 9x13 inch baking dish.
Bring a large pot of salted water to a boil. Add the elbow macaroni and cook until al dente. Drain well.
Return the hot pasta to the pot and immediately stir in the cubed unsalted butter until fully melted.
In a separate bowl, whisk together the evaporated milk, eggs, black pepper, and mustard powder until smooth.
Pour the milk mixture over the pasta, add 2 cups of the shredded sharp cheddar cheese, and stir until evenly combined.
Transfer the mixture to the prepared baking dish. Spread it out evenly and top with the remaining 2 cups of sharp cheddar cheese.
Bake uncovered for 45 minutes until the cheese is bubbly and golden brown on top. Let rest for 10 minutes before serving.