Prepare the Potatoes:
Place the potato slices in a large bowl of cold water to prevent browning. Drain and pat them dry with a paper towel.
Make the Cream Mixture:
In a saucepan, combine the heavy cream, whole milk, minced garlic, dried thyme, butter, salt, and black pepper. Heat the mixture over medium heat until it’s warmed through and the butter is melted. Do not let it boil.
Layer the Potatoes:
Grease a baking dish with butter or cooking spray. Place a layer of potato slices on the bottom of the dish, slightly overlapping them.
Add Cheese and Cream:
Sprinkle a portion of the grated Parmesan and Gruyere cheeses over the layer of potatoes. Drizzle some of the cream mixture over the cheese.
Repeat the Layers:
Repeat the process of layering potatoes, cheese, and cream until you’ve used up all the ingredients. Make sure to finish with a layer of cheese and cream on top.
Bake:
Cover the baking dish with aluminum foil and bake in the preheated oven for about 45-50 minutes. Then, remove the foil and continue baking for an additional 15-20 minutes, or until the top is golden brown and the potatoes are tender when pierced with a fork.
Serve:
Remove the Potatoes Delmonico from the oven and let it cool slightly before serving. Garnish with chopped fresh parsley for a burst of color and added freshness.