Preheat the oven to 200°C and line a baking sheet with parchment paper.
Place the raspberries in a small saucepan. Add the date syrup and cornflour, and stir gently over low heat for a few minutes until the mixture becomes slightly thickened and syrupy, but not fully jam-like. Remove from the heat and allow to cool.
Unroll the puff pastry and, using a mug or round cutter, cut circles from the pastry. Place them on the prepared baking sheet, leaving some space between each one.
Spoon a small amount of the raspberry mixture into the centre of each pastry round. Sprinkle the chopped dark chocolate over the raspberries.
Gently fold the edges of the pastry slightly inward all around to create a rustic tart shape, leaving the centre exposed.
Bake for 12–15 minutes, until the pastry is puffed and golden.
While the tarts are baking, melt some additional dark chocolate if you wish to drizzle them.
Once baked, allow the tarts to cool slightly. Drizzle with melted chocolate or dust with icing sugar before serving.