Heat the sugar and measurement water in a large ovenproof frying pan until golden and caramel coloured. Carefully add the butter and swirl around the pan until melted.
Meanwhile, cut out 4 rounds from the pastry using a 7 cm (3 inch) cookie cutter.
Carefully arrange the banana slices in 4 circles in the caramel, then place a pastry round on top of each. Place in a preheated oven, 220°C (425°F), Gas Mark 7, for 15 minutes until puffed and cooked through. Use a spatula to turn out of the pan and drizzle with the remaining sauce.