Roll out pastry to 1/8-inch thickness. Cut off a 4-inch strip and set aside to use as decoration.
Cut Brie in half making 2 layers, spread the nuts over one layer and cover with the other layer.
Sprinkle top w/ nuts.
Place brie in center of puff pastry and bring up edges and crimp edges together around brie, sealing completely. Turn brie, crimped dough side down, on to a baking sheet.
When ready to bake, remove plastic wrap. Mix egg yolk with 1 teaspoon water and brush entire dough covered brie.
Preheat oven to 400 degrees F. Bake for 15 to 20 minutes. Remove from oven and let sit 20 to 25 minutes before serving. Serve with cut fresh fruit, toasts, crackers, or other crudités.