1. Heat the oven to 400°F. Coarsely mash the bananas and syrup in a medium bowl with a fork.
2. Unfold 1 pastry sheet on a lightly floured surface. Cut the pastry sheet in half lengthwise. Roll each piece into a 15x5-inch rectangle. Cut each rectangle crosswise to make 3 (5-inch) squares. Repeat with the remaining pastry sheet, making 12 in all.
3. Spoon the banana mixture into the center of the pastry squares. Fold the corners to the center over the filling and twist tightly to seal. Place the filled pastries onto a baking sheet.
4. Stir the sugar and cinnamon in a small bowl. Brush the pastries with the milk and sprinkle with the sugar mixture.
5. Bake for 15 minutes or until the pastries are golden brown. Remove the pastries from the baking sheet and let cool on wire racks for 10 minutes.