Preheat the oven to 375°F (190°C) and lightly grease a 9×13-inch baking dish.
In a large bowl, whisk together the melted butter, cream cheese, sour cream, milk, garlic powder, onion powder, salt, and pepper until smooth.
Add the thinly sliced potatoes and gently toss to coat every slice evenly.
Stir in 1½ cups of the shredded cheese.
Transfer the mixture to the prepared baking dish and spread it evenly.
Cover tightly with aluminum foil and bake for 45 minutes, or until the potatoes are tender.
Remove the foil, sprinkle the remaining ½ cup of cheese on top, and bake uncovered for 15–20 minutes, until golden and bubbly.
Rest for 5–10 minutes before serving.
Garnish with fresh chives if desired.