Preheat your oven to 400 °F (about 200 °C). While it warms, spread the mini phyllo pastry shells out on the rimmed baking sheet in a single layer, giving each shell some breathing room.
Slice the Brie round into 24 little chunks. Place one piece of Brie into each phyllo shell. Then spoon about one teaspoon of cranberry sauce atop each Brie piece. Finally, sprinkle chopped pistachios over each bite.
Slide the tray into the hot oven and bake just until the cheese melts and becomes bubbly (about 6 minutes). Once done, serve them right away to keep the shells crisp and the centers gooey.