Preheat your oven to 190°C (375°F) and line a baking sheet with parchment paper.
Unfold the thawed puff pastry sheet and cut it into small squares or circles that fit snugly into your mini muffin tin cups.
Press each pastry piece gently into the cups, forming little cups or shapes that can hold filling without spilling over.
Bake the pastry shells for about 8 minutes, until they just start to turn golden and puff slightly.
While the pastry bakes, combine the cranberries, water, and sugar in a small saucepan. Bring to a simmer over medium heat, stirring occasionally.
Simmer for about 5 minutes or until the cranberries burst open and the sauce thickens slightly, filling your kitchen with a tangy aroma.
Remove the pastry shells from the oven and carefully spoon a small cube of brie into the center of each hot shell.
Top each with a spoonful of the warm cranberry sauce, letting it overflow slightly if needed.
Return the tray to the oven and bake for another 7 to 10 minutes, until the cheese has melted into a gooey, bubbling layer and the pastry edges are crispy.
Remove from the oven and let sit for 2 minutes. Garnish with a sprig of thyme or a sprinkle of fresh herbs, if desired.
Serve warm and enjoy the delightful combination of flaky pastry, creamy cheese, and tart cranberries in every bite.