Grease a 10x7 baking dish with oil or butter. Preheat oven to 350°F
Peel and slice potatoes. Take the potatoes and place evenly into bottom of pan, layering as you go.
In a small sauce pan, heat up the butter and truffle oil, add the flour and whisk until you have no lumps. Next add the milk, salt + pepper, garlic + onion powder and parmesan cheese. Whisk everything and bring to low simmer, you will end up with a nice thick sauce.
Drizzle the sauce over the sliced potatoes, making sure everything is well covered. Sprinkle on the both the cheddar cheeses and cover the pan with foil and bake for 30-40 min until potatoes are fork tender. Enjoy!