Preheat your oven to 400°F (200°C) and grease a medium-sized ceramic baking dish with butter.

Thinly slice the Yukon Gold potatoes to about 1/16th inch thick.

Melt 4 tablespoons of unsalted butter in a large pot over medium heat, then add 2 cloves of minced garlic and cook until fragrant.

Stir in 1/4 cup of all-purpose flour to create a roux, cooking for about 1-2 minutes without browning.

Pour in 2 cups of heavy cream, stirring continuously until thickened and gently bubbling, around 5 minutes.

Remove from heat and mix in 1 cup of Parmesan cheese, 1 teaspoon of fresh thyme, 1 teaspoon of kosher salt, and a pinch of black pepper.

Toss the sliced potatoes gently in the creamy sauce until evenly coated.

Layer the coated potato slices upright into the greased baking dish, pouring any remaining sauce on top.

Cover with aluminum foil and bake for 30 minutes, then remove the foil and bake uncovered for another 30 minutes.

Let cool for about 10 minutes before serving.