Heat up the tin for approx. 5 mins. in an oven preheated to 180°C. Boil the sugar in a wide pan without stirring. Reduce the heat and simmer, swirling the pan occasionally until a light brown caramel has formed. Remove the pan from the heat. Pour the caramel into the preheated tin. Scatter the cubes of butter on top.
Arrange the bananas in the tin with the cut sides facing up. Firmly prick the pastry with a fork and lay loosely over the bananas. Make a rim between the bananas and the edge of the tin.
Approx. 30 mins. in the centre of an oven preheated to 180°C. Remove from the oven, leave to stand for approx. 2 mins., separate the tart from the edge of the tin with a knife, carefully tip out onto a cake plate, remove the baking paper.
Mix the double cream with the cinnamon, spread a little on top of the tart, sprinkle the nuts on top. Serve with the remaining double cream.