Fold a 45cm long rectangle of aluminum foil into triangles until you have a triangle with a longest side of 10-12cm. Form this triangle into a cone. Make as many aluminum cones as you want.
Cut a sheet of puff pastry into 2.5cm strips. Wrap the pastry around an aluminum cone so that it overlaps by about 1 cm. Press the tail of the pastry onto itself so that it sticks. Lay this seam face down on a baking sheet. Bake for 18-20 minutes at 180°C.
Whip 500ml of double cream. Reserve 2-3 large scoops of whipped cream. Mix the remaining whipped cream with 200 ml of toffee. Scoop this into a plastic bag for piping.
Pipe cones by alternating 2cm of toffee cream and 1 slice of banana. Top with a swirl of reserved cream and a vertical banana slice.