Preheat your oven to 375°F (190°C) and grease a 2-quart baking dish with butter.
In a medium saucepan, combine heavy cream, minced garlic, fresh thyme leaves, salt, and black pepper. Heat over medium until it simmers, then remove from heat.
Layer half of the sliced potatoes in the greased baking dish, slightly overlapping. Pour half of the cream mixture over the potatoes and sprinkle half of both cheeses on top.
Repeat with the remaining potato slices, cream mixture, and cheeses.
Cover the dish with aluminum foil and bake for 45 minutes.
Remove the foil and bake uncovered for an additional 30 minutes, until the potatoes are fork-tender and the top is golden brown.
Let the dish cool for 5-10 minutes before slicing.
Garnish with finely chopped fresh chives before serving.
Notes
For a rustic presentation, serve directly in the baking dish.