Preheat the oven to 425 degrees F. Lightly coat a baking sheet with cooking spray.
Place the halved potatoes in a pile on the baking sheet. Pour the olive oil over the potatoes, and sprinkle the rosemary, salt and pepper over top. Using tongs or your hands, toss the potatoes until coated.
Arrange the potatoes in a single layer on the baking sheet, cut side down. Roast until the potatoes are tender when pierced with a fork, about 25 minutes.
While the potatoes are roasting, cut the Brie cheese into 36 thin squares.
Once the potatoes are cooked, flip them over so they are cut side up and place a piece of Brie cheese on each potato. Return to the oven until the cheese is melted, about 3 minutes.
Top each potato bite with ¼ teaspoon cranberry and 1 rosemary leaf. Serve.