Set your oven to 375°F (190°C) and lightly grease a baking dish with butter or nonstick spray.
Peel and thinly slice the potatoes evenly (about 1/8 inch thick) using a sharp knife or mandoline for consistent cooking.
In a saucepan, melt unsalted butter over medium heat.
Add the minced garlic and sauté until fragrant. Stir in heavy cream, garlic powder, onion powder, paprika, salt, and pepper. Bring the mixture to a gentle simmer and remove from the heat. Add in the cheese and mix.
Arrange a layer of sliced potatoes in the baking dish, slightly overlapping.
Pour a portion of the cream sauce over the layer, then sprinkle with a mix of mozzarella and cheddar cheese.
Repeat layers until all ingredients are used, finishing with cheese on top.
Cover the dish with aluminum foil and bake for 40-50 minutes, until the potatoes are tender.
Remove the foil and bake for an additional 15-20 minutes, allowing the cheese to turn golden and bubbly.
Let the gratin rest for 10 minutes to set. Sprinkle fresh parsley on top for a burst of color and serve warm.
