Heat the oven to 180c/fan 160c/gas 4. Sprinkle the sugar over the base of a 25cm diameter oven-proof frying pan or 4 blini pans and cook over a medium heat until the sugar melts and you create a nice goldenbrown caramel. Tip each pan from side to side to keep the caramel even. Remove from the heat and add the butter.
Cut the bananas into big chunks and arrange over the caramel. Roll out the puff pastry and trim to fit the width of the pan or pans. Lay the puff pastry sheet over the bananas and tuck the edges down and around the inside of the pan. Make a small hole in the middle of the pastry with a knife to let the steam out. Bake for 20-30 minutes or until the pastry is puffed and golden. Cool for 10 minutes.
To release the tatin, place a plate on the top of the pan and turn upside down. Serve with ice cream.