Preheat your oven to 400 degrees Fahrenheit. Line a large baking sheet with parchment paper or a silicone baking mat to prevent the pastry from sticking. Thaw your puff pastry according to the package directions, but keep it in the refrigerator until the very moment you are ready to use it, as cold dough rises better and stays easier to handle.
Unroll the puff pastry sheet on a lightly floured surface. Use a star-shaped cookie cutter or a sharp knife to cut out 12 small shapes that are slightly larger than the diameter of your mini brie rounds. If you want a more literal tree look, you can cut the pastry into small triangles instead. Place these pastry shapes onto your prepared baking sheet with about an inch of space between them.
Place one mini brie round in the center of each pastry shape. If your brie rounds have a very thick rind, you can gently slice off the top layer to help the cheese melt more evenly, though the rind is entirely edible. Top each piece of cheese with a small teaspoon of cranberry sauce, pressing it down slightly so it stays in place during the baking process.
Using a pastry brush, lightly coat the exposed edges of the puff pastry with the egg wash. This step is essential for achieving that beautiful golden-brown color and a professional shine. Sprinkle a tiny pinch of sea salt over the pastry. Place the tray in the oven and bake for 10 to 12 minutes, or until the pastry has puffed up significantly and turned a rich golden color.
Remove the tray from the oven and let the bites cool for just two minutes. While they are still warm, insert a small sprig of fresh rosemary into the top of each brie round to act as the “tree.” Sprinkle a few pomegranate seeds around the base of the rosemary to look like festive ornaments. Serve them while the cheese is still beautifully melted and soft.
