In a large mixing bowl, toss the sweet potatoes with the olive oil, oregano, salt, pepper, chipotle powder and garlic until the potatoes are evenly coated. Arrange the sweet potatoes in a 9 1/2-inch round glass baking dish, arranging in overlapping, concentric circles, until the dish is filled. Cover with foil and bake until tender, about 30 minutes.
Remove the foil and add the cream. Return the casserole to the oven and continue baking, uncovered, until golden with crisp edges another 20 minutes. Serve warm.