Heat the oven to 350°F. Meanwhile, stir ⅓ cup whole berry cranberry sauce, 2 tablespoons packed brown sugar, 1 teaspoon vanilla extract, 1 teaspoon finely grated orange zest, and ⅛ teaspoon ground nutmeg together in a small bowl.
Place 1 (8-ounce) cold brie cheese round in a small baking dish or pie plate if you plan to serve it out of the dish. If you’d like to transfer the cheese to a serving dish or platter after it’s baked, line it with parchment paper first.
Spoon the cranberry mixture over the top. Sprinkle with 2 tablespoons coarsely chopped nuts. Top with 1 of the fresh rosemary sprigs if desired.
Bake until the cheese feels soft when gently poked, 8 to 15 minutes. Do not bake until oozing, completely melted, or collapsed.
If desired, lift the parchment paper and use a spatula to carefully slide the cheese onto a serving dish. Discard the rosemary sprig and replace it with a fresh rosemary sprig if desired. Serve immediately with assorted crackers.
