Preheat the oven to 375 F (190 C).

In a medium-sized pot, melt the butter together with the sweet whipping cream and grated Parmesan cheese for 4-5 minutes until all the butter is melted and the mixture starts to slightly simmer. Add the potato slices to the pot and gently stir for 2-3 minutes while simmering.

Turn off the heat and add salt and thyme. Gently mix with a spatula, being careful not to break the delicate slices. Transfer to a baking dish. Smooth out the mixture in the dish and sprinkle the cheeses. Bake for 70 minutes, or until the top is golden and the potatoes are completely tender all the way down to the bottom of the pan.