Preheat your oven to 190°C (375°F) and line a baking sheet with parchment paper.
Unfold the puff pastry sheet on a lightly floured surface and use a sharp knife or pizza cutter to cut it into 24 small squares, about 2 inches each.
Gently transfer the pastry squares onto the prepared baking sheet, spacing them out evenly.
Place a small slice of brie cheese and a few cranberries on top of each pastry square.
Bake in the preheated oven for 12-15 minutes, or until the pastry is golden and puffed, and the cheese is bubbling.
Remove from the oven and let the bites rest for about 5 minutes to allow the cheese to set slightly.
Garnish with a small sprig of thyme or a pinch of sea salt if desired, then serve warm and enjoy the festive flavors.