Preheat your oven to 350°F (175°C). Gather your ingredients as the oven heats up.

Peel the potatoes and slice them into even 1/8-inch rounds, placing them in cold water to prevent browning.

Finely dice the onion and mince the garlic, setting aside for sautéing.

In a large pot, melt the butter over medium heat, then sauté the onion for about 5–6 minutes.

Stir in the minced garlic and cook for an additional minute until fragrant.

Sprinkle in the flour, stirring continuously for 1–2 minutes to form a roux.

Gradually whisk in the milk and cream, stirring until the sauce thickens (5–8 minutes).

Add salt, black pepper, nutmeg, and mix in the cheeses until fully melted.

Drain the potato slices and fold them into the cheese sauce carefully.

Pour the mixture into a greased 9x13-inch baking dish and sprinkle additional cheese on top.

Cover with foil and bake for 1 hour, then uncover and bake for an additional 20 minutes until crispy.

Allow to rest for 5 minutes, then garnish with parsley before serving.