Bring a large pot of salted water to a boil. Add the macaroni and cook until al dente according to package instructions. Drain and set aside.
In a large mixing bowl, combine the grated cheddar cheese and grated Parmesan cheese.
In a separate bowl, mix the evaporated milk, beaten eggs, chopped onion, chopped bell pepper, minced garlic, Dijon mustard, paprika, ground black pepper, salt, and cayenne pepper (if using). Stir well to combine.
Preheat your oven to 350°F (175°C).
Grease a baking dish with butter.
In a large bowl, combine the cooked macaroni with the cheese mixture, ensuring the pasta is well coated.
Pour the macaroni mixture into the greased baking dish. Smooth the top with a spatula.
Sprinkle the breadcrumbs evenly over the top of the macaroni mixture.
Drizzle the melted butter over the breadcrumbs.
Bake in the preheated oven for about 30-35 minutes, or until the top is golden brown and the pie is set.
Remove from the oven and let it cool slightly before serving.
Slice the macaroni pie into squares and serve warm as a side dish or main course.
Enjoy your meal!