Preheat your oven to 350°F (175°C).

Wash and peel the potatoes, then slice them into 1/8-inch rounds.

In a medium saucepan, melt butter, add onion, garlic, and thyme, and sauté for 3-5 minutes.

Sprinkle flour over the mixture and stir continuously for 1 minute. Gradually whisk in milk.

Remove from heat and stir in cheese, nutmeg, salt, and pepper until melted.

Butter a baking dish, layer potatoes and pour cheese sauce in between layers.

Sprinkle remaining cheese on top before baking.

Cover with foil and bake for 45-60 minutes until potatoes are tender.

Remove from oven, let rest for 10 minutes before serving.