Preheat the oven to 325°F.
Bring a large pot of water to a rolling boil. Add enough salt to make it taste like the ocean. Add the pasta and cook it until it's al dente, about 7 minutes. Drain the pasta.
In a large bowl, whisk together the eggs, seasoned salt, and pepper. Pour in the evaporated milk and whisk until well combined. Set aside.
Return the drained pasta to the pot, and while it's still hot, stir in the butter until fully melted.
Add the cubed cheddar cheese to the pot and stir until the cheese starts to melt. Then add the shredded mozzarella or gruyere and mix again.
Pour the egg and milk mixture into the pasta and cheese. Stir until everything is well combined.
Pour the mixture into a 13x9-inch glass casserole dish and spread it out evenly. Bake in the preheated oven for 15 minutes.
Remove and stir the mixture gently to ensure even baking. Top with the shredded cheddar cheese.
Return the dish to the oven and bake for another 15 minutes, or until the cheese on top is fully melted and the eggs have set.
Optional: For the last 5 minutes, switch to the high broil setting to toast the cheese and give you crispy edges.
Remove from the oven and let the mac and cheese rest for at least 15 minutes before serving to allow it to firm up.