Melt the sugar, butter and rum together in a 23cm cast iron pan over a low heat, stirring until the sugar has melted. Turn up the heat and bubble the mixture until it turns a golden caramel colour, then remove from the heat and stir in the cinnamon.
Slice the bananas into 2cm-thick pieces and arrange them in concentric circles in the pan.
Cut the pastry into a circle 3cm larger than the skillet. Lay the pastry on top of the bananas and tuck the edges down inside the tin. Bake in the oven for 25-30 mins until the pastry is risen and cooked through.
Leave the tart to cool in the tin for 5 mins, then carefully turn the tart out onto a large plate. Wait a further 5 minutes before slicing and serving.
