Preheat the oven to 375°F (190°C) and lightly grease a baking dish.Bring a large pot of water to a boil and cook the sweet potato slices until just tender, about 10–15 minutes. Drain well.Layer half of the sweet potatoes evenly in the baking dish.Sprinkle half of the cranberries over the sweet potatoes.In a bowl, mix the cooking cream, brown sugar, cinnamon, salt, and pepper. Pour half of the mixture over the layers.Repeat the layers with the remaining sweet potatoes, cranberries, and cream mixture.Sprinkle the top evenly with Gruyère cheese and breadcrumbs.Bake the Sweet Potato Cranberry Gratin for 30–35 minutes, until golden, bubbly, and lightly crisp on top.Let rest for a few minutes before serving.