Preheat the oven to 375°F (190°C).
Grease a 9x13-inch baking dish with butter or cooking spray.
In a saucepan, melt the butter over medium heat. Add the minced garlic and sauté for 1-2 minutes.
Pour in the heavy cream and milk. Stir, then bring to a simmer.
Once simmering, reduce heat and add in the cheddar cheese and Parmesan cheese, stirring until the cheese is melted and the mixture is smooth.
Season with salt and pepper to taste.
Arrange the sliced potatoes in the greased baking dish, layering them evenly.
Pour the cheese sauce over the potatoes, ensuring they are evenly covered.
Cover the dish with aluminum foil and bake for 45 minutes.
Remove the foil and bake for an additional 20 minutes, or until the potatoes are tender and golden on top.
Garnish with fresh parsley (optional) and serve hot.