Preheat your oven to 375°F (190°C) and prepare your baking dish by greasing it lightly.

Peel and slice sweet potatoes into 1/4 inch thick discs. Boil them in salted water for 10-15 minutes until tender, then drain.

Layer half of the cooked sweet potatoes in the greased baking dish. Sprinkle half of the cranberries over the sweet potatoes.

In a mixing bowl, combine heavy cream, brown sugar, cinnamon, salt, and pepper. Whisk until smooth and pour half over the layered ingredients.

Repeat the layering with the remaining sweet potatoes and cranberries, and pour the remaining cream mixture over top.

Sprinkle shredded Gruyère cheese and breadcrumbs over the gratin.

Bake in the preheated oven for 30-35 minutes until bubbly and golden brown.

Let it cool for 5-10 minutes before serving.