Preheat the Oven:
Preheat your oven to 350°F (175°C). Lightly grease a 9×13-inch (23×33 cm) baking dish with butter, oil, or non-stick cooking spray.

Make the Cream Mixture:
In a large bowl, whisk together the heavy cream, mayonnaise, sour cream, garlic powder, onion powder, salt, and pepper until smooth.

Prepare the Potatoes:
Using a mandoline or a sharp knife, slice the potatoes very thinly and evenly. Keep the slices uniform so they cook evenly.

Assemble the Layers:
Spread a few spoonfuls of the cream mixture on the bottom of the baking dish.
Layer one-third of the potato slices evenly in the dish.
Sprinkle one-third of both cheeses over the potatoes, then spoon one-third of the cream mixture on top.
Repeat the process two more times until all ingredients are used. Finish with an extra layer of cheese on top.

Bake the Casserole:
Cover with foil (spray the underside with a little cooking spray to prevent sticking) and bake for 1 hour.
Remove the foil and bake uncovered for another 15–20 minutes, until the top is golden and bubbling.

Check Doneness:
Insert a knife or fork into the center — if it slides in easily, the potatoes are fully cooked.

Serve:
Let the dish rest for about 10 minutes before serving. Garnish with chopped parsley or green onions for a fresh finish.