Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.

In a mixing bowl, combine the finely chopped pistachios, honey, chopped fresh rosemary, sea salt, and freshly cracked black pepper until well combined.

Roll out the chilled puff pastry on a lightly floured surface until about 1/8 inch thick. Cut into square pieces measuring approximately 3x3 inches.

Position a piece of Brie cheese in the center of each pastry square, topping with 1-2 teaspoons of the pistachio mixture. Fold corners of the pastry over the Brie and pinch to secure.

Beat the egg to create an egg wash and lightly brush the tops of each assembled bite with it.

Bake the Brie bites in the preheated oven for 15-20 minutes, or until the pastry is puffed and golden brown.

Allow to cool slightly, then garnish with fresh cranberries or pomegranate seeds if desired. Serve warm.