Preheat your oven to 375°F (190°C).
Roll out the puff pastry sheet and cut it into 24 equal squares.
Apply some butter to the cupcake tray and lay each piece of puff pastry on the tray.
Place a small piece of Brie and a small dollop of cranberry sauce in the center of each pastry square.
Bake for about 12-15 minutes, or until they turn golden brown and puffy.
Remove from the oven and let cool slightly. Garnish with fresh rosemary or thyme if desired. Serve your Cranberry Brie Bites warm.