Preheat the oven to 350 degrees F. Grease a large casserole dish.
Melt 2 tablespoons butter in a saucepan over medium heat. Add milk, bring to a simmer, then reduce heat to low. Mix flour with 2 to 3 tablespoons water until smooth. Add flour mixture to the saucepan, stirring constantly, and cook until sauce thickens. Add cubed extra-sharp Cheddar and cubed sharp Cheddar cheese, stirring until cheese melts. Remove from heat.
Meanwhile, bring a large pot of salted water to a boil, and cook elbow macaroni until al dente (tender with a bite), about 8 minutes, or according to package instructions. Drain and set aside.
Melt remaining 2 tablespoons butter in a microwave-safe bowl on High, about 10 seconds. In a large bowl, combine elbow macaroni, melted butter, and eggs. Stir in cheese sauce; adding a little more milk if the sauce seems too thick. Season with salt and pepper.
Pour macaroni and cheese into the prepared casserole dish. Top with shredded cheese and seasoned breadcrumbs.
Bake in the preheated oven until golden-brown and bubbling, 35 to 45 minutes.
