Preheat the oven to 375°F. Lightly spray a 9×13 inch baking pan.
Bring a large pot of salted water to a boil. Add the macaroni and cook until al dente. Drain and return to the pot.
Stir in the butter until melted. Set aside.
In a large bowl, whisk together evaporated milk, milk, eggs, and garlic salt until fully combined.
In a separate bowl, mix together the cheddar and mozzarella cheeses.
Layer 1/3 of the macaroni in the prepared baking pan, then 1/3 of the cheese mixture. Repeat with the remaining macaroni and cheese mixture.
Pour the milk mixture evenly over the top. Sprinkle with paprika.
Bake for 25-30 minutes, or until bubbly and golden brown.