Preheat the oven to 200C/400F/Gas 6. Grease a 12-hole petit four tin
For the pastry, place the flour, butter, sugar and salt into a food processor and pulse until the mixture resembles breadcrumbs. Add the egg yolks and enough cream to bring the mixture together to form a dough. Wrap the dough in cling film and place in the fridge for at least 30 minutes.
Meanwhile, make the toffee. Heat the sugar and butter in a pan until the sugar has dissolved then stir in the cream and pour the mixture into a bowl. Set aside to cool.
Roll the pastry out on a floured work surface, cut out 12 circles and use them to line the holes of the petit four tin. Bake in the oven for 12-16 minutes or until the pastry is golden-brown and crisp. Carefully transfer the pastry cases to a wire rack and set aside to cool.
For the mousse, mash the bananas with a hand held blender. Whip the cream until it holds soft peaks then fold in the bananas and the sugar. Pour into a bowl and chill in the fridge.
To assemble, spoon a little toffee into each pastry case. Spoon the mousse into a piping bag fitted with a plain nozzle and pipe on top of the toffee. Scatter over the shaved chocolate.