Preheat the oven to 375 degrees.
In a large bowl, combine the heavy cream, cheese sauce, cheeses, garlic, onion powder, garlic salt, black pepper, and kosher salt and mix well.
Wash and slice the potatoes into 1⁄8-inch-thick slices and place immediately into the sauce mixture. Mix by hand to coat all the surfaces of the sliced potatoes.
Place the mixture in a 9 by 13-inch baking dish and cover tightly with aluminum foil. Bake for about 1 hour.
Uncover and bake for 20 to 30 minutes longer, until the top is golden brown.
Let cool, garnish with fresh parsley, and serve.