Preheat the oven to 350°F (175°C). Grease a baking dish with butter.
In a saucepan, combine melted butter, heavy cream, minced garlic, salt, and pepper. Heat gently until the mixture is warmed through.
Layer the thinly sliced potatoes evenly in the baking dish, overlapping slightly.
Pour a portion of the cream mixture over the potatoes, ensuring it seeps into the layers.
Repeat layering potatoes and pouring cream mixture until all ingredients are used, finishing with a layer of cream mixture on top.
Cover the dish with foil and bake for 45 minutes. Remove the foil and bake for an additional 25-30 minutes or until the top is golden brown and potatoes are tender.
Let it rest for 10 minutes before garnishing with fresh thyme leaves. Serve warm.