To begin, thinly slice the potatoes using a mandoline to ensure equal thickness. Soak them in water so that they do not colorize.
To prepare the Bechamel sauce, melt butter on medium heat in a saucepan.
Add in the flour whisking constantly until cooked. Do not brown.
Next, add in the milk and the cream whisking constantly making sure no lumps are formed.
Now add in the seasoning - salt to taste, garlic powder, onion powder, and black pepper powder. Simmer until the sauce thickens and coats the back of the spoon.
Turn off the heat. Add in the cheese. Fold it in until the cheese melts. Keep aside.
In the meantime, preheat the oven to 180°C or 350°F.
To assemble, grease the baking dish with butter. Stack the potato slices and arrange them in rows. Pour the cheesy Bechamel sauce on top.
Cover with aluminum foil and bake in a preheated oven at 180°C or 350°F for 25-30 minutes.
Remove the foil. Sprinkle some grated cheese on top. Bake it for another 20-25 minutes until done and the sauce and cheese colorize.
Remove from oven and let it stand for 5-10 minutes so that the sauce settles.
The Potatoes Au Gratin is ready to serve.