Preheat your oven to 375°F (190°C).
Peel the potatoes and slice them into thin rounds, about ⅛ inch thick. Rinse the potato slices in cold water and drain.
In a large pot, bring water to a boil over medium-high heat. Add the sliced potatoes and cook for 5-7 minutes until slightly tender but not fully cooked. Drain the potatoes and set aside.
In a mixing bowl, combine the heavy cream, milk, garlic powder, onion powder, salt, and black pepper. Whisk until well blended.
Grease the baking dish with butter. Layer half of the potato slices in the dish, then pour half of the creamy mixture over them. Sprinkle half of the cheddar cheese on top.
Repeat with the remaining potato slices, creamy mixture, and cheese.
Sprinkle the grated Parmesan cheese evenly over the top.
Cover the baking dish with aluminum foil and bake in the preheated oven for 30 minutes.
Remove the foil and bake for an additional 15 minutes, or until the cheese is bubbly and golden brown, and the potatoes are tender when pierced with a fork.
Allow the dish to cool for a few minutes before serving. If desired, garnish with fresh chives.