Pre-heat the oven to 375 degrees. Lightly mist a 24-cup mini-muffin tin with cooking spray and set aside.
On a clean, dry cutting board lay down your sheet of defrosted puff pastry. Using a knife (or a pizza cutter), cut the dough into 24 equal squares. Press each pastry square into a well of the mini-muffin tin to form a cup. If the pastry has warmed to room temperature, place the tin in the refrigerator for 10 minutes to re-chill. Place the tin in the oven and bake for 10 minutes.
While the pastry cups are baking, mist a small saucepan with cooking spray and bring to medium heat. Add the cranberries and cook, uncovered, for 5 minutes, stirring occasionally. While the cranberries are cooking, combine the water and cornstarch in a dish and stir until well combined. Add the cornstarch slurry and the sugar to the cranberries and stir until well combined. When the mixture begins to bubble (should happen quickly), cover the pot and reduce the heat to low. Cook on low for 3-5 minutes until mixture is thickened. Remove from heat and stir.
When the cups are finished baking, press the end of a wooden spoon into the center of each cup to form a well in the pastry. Spoon the cranberry sauce into the pastry cups, distributing the sauce evenly between the cups. Place a cube of brie on top of each cup and sprinkle with a bit of thyme. Return the tin to the oven and bake for another 5-7 minutes until brie is melted and cups begin to turn golden. Remove from the oven and allow to sit for a few minutes before removing from the tin.