Preheat the oven to 350 degrees F (175 degrees C). Pour melted butter into a glass 9x13-inch baking dish. Tilt the dish to coat the bottom with butter.

Beat eggs, Cheddar, seasoned salt, hot sauce, and mustard powder together with a whisk in a large bowl. Stream milk into egg mixture while whisking; pour into the baking dish.

Bake in the preheated oven for 15 minutes. Stir, then continue to bake until eggs are set in the middle, 15 to 20 more minutes. Serve immediately.