Preheat the oven to 350°F. Spray a 9x13-inch glass baking dish with nonstick cooking spray.
In a large bowl, crack 12 large eggs. Add 1 cup milk, 1/4 cup water, 1 teaspoon salt, and 1/4 cup melted, cooled butter.
Whisk the mixture until well blended and uniform.
Pour the egg mixture into the prepared baking dish and spread it evenly.
Bake uncovered for 10 minutes.
Remove the dish from the oven and gently stir the eggs with a spatula to break up any set edges and mix partially cooked portions.
Return the dish to the oven and bake an additional 12 minutes, or until the eggs are mostly set and no longer runny (they should be moist but cooked through).
Remove from the oven, let rest 1–2 minutes, then fluff with a fork and serve warm.