Preheat oven to 375°F. Grease a 9x13 baking dish so nothing sticks.
Toss sliced potatoes with olive oil, melted butter, salt, pepper, garlic powder, thyme, and rosemary.
Layer half the potatoes in the dish, sprinkle half the Parmesan and half the mozzarella.
Add remaining potatoes and top with remaining cheeses. Sprinkle panko if using.
Cover tightly with foil and bake 35 minutes. Remove foil and bake 10–15 more minutes until potatoes are tender and top is golden.
Let rest 5 minutes before serving. I cut into squares—easy to pass around.