Start by preheating your oven to 400°F and lining a baking sheet with parchment paper. Cut the brie into small bite-sized cubes and keep them chilled until ready to use. Finely chop the pistachios and mince the rosemary so everything blends evenly.
In a medium bowl, combine the chopped pistachios, honey, rosemary, sea salt, and black pepper. Stir everything together until the nuts are lightly coated with honey. This mixture creates the crunchy, flavorful topping that makes the bites special.
Lightly flour your countertop and roll out the puff pastry to about 1/8-inch thickness. Cut the pastry into even 3-inch squares using a sharp knife or pizza cutter. Keeping the pastry cold helps it stay flaky during baking.
Place one cube of brie in the center of each pastry square. Spoon a small amount of the pistachio mixture on top of the cheese. Be careful not to overfill the pastry or the cheese may leak while baking.
Fold the corners of each pastry square toward the center and pinch gently to seal. Place the sealed side down on the prepared baking sheet. This helps the bites stay closed and hold their shape while baking.
Beat the egg in a small bowl until smooth and brush it over the tops and sides of each pastry bite. The egg wash gives the pastry a beautiful golden finish. It also helps create a crisp texture during baking.
Bake the brie bites for 15 to 20 minutes until the pastry is puffed and golden brown. The cheese inside should become soft and creamy without completely leaking out. Keep an eye on them during the final few minutes because puff pastry browns quickly.
Allow the bites to cool for about 5 minutes before serving. Sprinkle pomegranate seeds or dried cranberries over the top for color and freshness. Serve warm so the brie stays perfectly melty and delicious