Heat oven to 190C/fan 170C/gas 5. Butter two 20cm sandwich tins and line with non-stick baking paper. In a large bowl, beat all the cake ingredients together including the vanilla extract and 2 mashed, ripe bananas, until you have a smooth, soft batter.
Divide the mixture between the tins, smooth the surface with a spatula or the back of a spoon, then bake for about 20 mins until golden and the cake springs back when pressed. Turn onto a cooling rack and leave to cool completely.
For the filling, whip the double cream and fold through the Banoffee toffee. To serve, spread half of the cream over one of the cakes, then top with another sliced banana.
Sandwich together, then cover with more cream then decorate the cake with an elegant drizzle of Banoffee toffee. Keep in an airtight container and eat within 2 days.