Preheat your oven to 375 degrees Fahrenheit. Line a standard mini muffin tin with non-stick spray or a light coating of butter. Ensure your puff pastry is thawed according to package directions but remains cold to the touch, as this ensures the most flakes during baking.
Unfold the puff pastry sheets onto a lightly floured surface. Use a pizza cutter or a sharp knife to cut each sheet into 12 equal squares, giving you 24 squares total. Cut the Brie cheese into small chunks, roughly one inch in size. It is helpful to keep the rind on as it helps the cheese hold its shape, but you can trim it if you prefer a smoother texture.
Place one pastry square into each cavity of the mini muffin tin, pressing down gently so the corners point upward. Place one piece of Brie in the center of each pastry cup. Top the cheese with a generous teaspoon of cranberry sauce. Sprinkle the chopped pecans and a pinch of fresh rosemary over the top of each bite.
Whisk the egg and water together in a small bowl to create an egg wash. Use a pastry brush to lightly coat the exposed edges of the puff pastry. Place the tin in the oven and bake for 15 minutes, or until the pastry is puffed and a deep golden brown. The cheese should be melted and bubbling slightly.
Remove the tin from the oven and let the bites rest for about 5 minutes. This allows the cheese to set slightly so they are easier to remove. Use a butter knife to gently lift each bite out of the tin and place them on a festive serving tray while still warm.
