Preheat your oven to 400°F and lightly coat a medium-sized ceramic baking dish with a bit of cooking spray.

Carefully slice the Yukon gold potatoes about 1/16 of an inch thick using a mandolin or sharp knife to ensure even cooking.

In a large pot over medium heat, melt the butter along with the minced garlic until fragrant, about 1-2 minutes.

Mix in the flour to form a roux and let it cook for a minute or two before pouring in the heavy cream, stirring until the mixture thickens, which should take around 5 minutes.

Stir in the Parmesan cheese, thyme, salt, and black pepper until well blended and smooth.

Remove from the heat and allow the sauce to cool slightly before moving to the next step.

In a large bowl, add the sliced potatoes and gently pour the creamy sauce over them, tossing to coat all slices evenly.

Arrange the coated potato slices upright in the prepared baking dish, pouring any remaining sauce over the top. Add a sprinkle of extra Parmesan if desired.

Cover with aluminum foil and bake in the preheated oven for 30 minutes. After that, remove the foil and continue baking for another 30 minutes, or until the potatoes are golden and tender.

Once done, let the dish cool for about 10 minutes before serving to allow the flavors to meld.