Line two 12-hole mini muffin tins with paper cases. Place all the cake ingredients except the toffees in a food processor and whiz until smooth, or beat in a large bowl. Then stir in the toffees.
Spoon the mixture into the paper cases, sprinkle over most of the muscovado sugar and place in a preheated oven, 200°C (400°F), Gas Mark 6, for 10–12 minutes until golden and just firm to the touch. Remove the cakes from the oven and cool on a wire rack.
Top with chewy banana slices or banana chips and sprinkle with the remaining sugar.