Wash, peel, and thinly slice the potatoes into uniform rounds, about 1/8 inch thick. Soak sliced potatoes in a bowl of water to prevent browning.

In a medium saucepan over medium heat, melt butter. Whisk in flour and cook for 2 minutes to form a paste.

Slowly add cream and milk, stirring until the sauce thickens (about 5-7 minutes). Mix in onion powder, garlic powder, salt, and pepper.

Preheat oven to 350°F (175°C). Grease a 9x13-inch baking dish with butter.

Layer a third of the sliced potatoes, followed by a third of the sauce, and a third of the shredded cheeses. Repeat twice, ending with a layer of cheese.

Cover with aluminum foil and bake for 45 minutes. Remove foil and bake for an additional 15-20 minutes until golden brown.

Allow to cool for 10-15 minutes before serving. Garnish with chopped parsley or dill.