Preheat your oven to 375°F (190°C).
Peel the potatoes and slice them thinly (about ⅛ inch thick) using a knife or mandoline. Place the sliced potatoes in a large mixing bowl and set aside.
In a saucepan over medium heat, melt the butter. Add the minced garlic and sauté until fragrant, about 1 minute.
Stir in the heavy cream, milk, onion powder, salt, black pepper, and paprika. Bring the mixture to a gentle simmer, whisking occasionally.
Remove the saucepan from heat and add the shredded cheddar cheese and grated Parmesan cheese. Stir until the cheeses are melted and the sauce is smooth.
In the prepared baking dish, layer half of the sliced potatoes. Pour half of the cheese sauce over the potatoes, ensuring they are evenly covered. Repeat with the remaining potatoes and cheese sauce.
Cover the baking dish with aluminum foil and bake in the preheated oven for 30 minutes.
After 30 minutes, remove the foil and bake for an additional 15 minutes or until the cheese is bubbly and golden brown.
Allow the dish to cool for a few minutes before serving. Garnish with additional cheese or fresh herbs if desired.