Preheat the oven to 400°F (200°C). Gather your ingredients and equipment.

In a mixing bowl, combine heavy cream and cornstarch. Whisk until smooth, then stir in melted butter, minced garlic, thyme, salt, and pepper.

Thinly slice sweet potatoes into 1/8-inch rounds, drizzling a bit of the cream mixture over slices to prevent browning.

Layer sweet potato slices in a prepared baking dish, drizzling cream mixture over each layer.

Pour the remaining cream mixture over the layered sweet potatoes.

Bake in the preheated oven for 30 minutes until bubbling.

Add shredded Parmesan cheese on top and return to the oven for another 10 minutes.

Remove from the oven and let cool slightly before serving.