Slice the bananas in half horizontally. Roll the pastry into a 20 cm (8 inch) square and cut the pastry into equal quarters. Place on a baking sheet and score a 1 cm (½ inch) border around the edge of each pastry square. Arrange the bananas, cut-side up, on the pastry inside the border, then brush the border with the beaten egg. Sprinkle the top of the bananas with the sugar.
Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 15–20 minutes or until the pastry is puffed and golden and the bananas are caramelized. Serve the tart hot with cream.