1. Cook the pasta according to package directions in salted water; drain and return shells to the pot.
2. Stir in the butter; cover, and set aside.
3. Position a boiler rack so that the top of your macaroni and cheese (in its baking dish) will be 4-6 from the heat source; preheat the broiler.
4. Meanwhile, whisk together the eggs, evaporated milk, Worcestershire sauce, salt, chili powder, and pepper until combined.
5. Place the pasta over low heat; stir in the milk mixture and 2 cups of the cheese.
6. Cook, stirring, until a creamy sauce forms and the mixture is hot, about 5 minutes.
7. Pour the mixture into an ungreases 6-cup baking dish; sprinkle with remaining cheese.
8. Broil until lightly browned and bubbly, 2-3 minutes; serve hot.