Place butter, sugar and cinnamon in a large flameproof roasting pan over medium heat on the stove top, stir until butter is melted and mixture is combined and caramelised. Turn off the heat.
Meanwhile, place two banana halves, cut-side down, onto a pastry sheet. Trim pastry around bananas, following the shape, leaving a 1.5cm border around each banana. Wrap pastry around curved banana halves. Repeat with remaining banana halves and pastry sheets.
Carefully place banana halves, cut-side down into the caramel mixture. Transfer to oven, bake for 20 minutes or until pastry is golden and cooked through. Stand for 5 minutes before carefully inverting tatins onto plates.