Preheat your oven to 400ºF (200ºC). Peel and cut sweet potatoes into thin slices.
Place garlic, oil, butter, salt, garlic powder, Parmesan cheese, Italian seasoning, and thyme leaves in a large bowl and mix well. Throw in sweet potatoes and mix until well coated.
Prepare baking dish and arrange coated sweet potatoes stacking them one on top of the other.