For the cashew brittle, grease a baking tray with a little butter.
Toast the cashew nuts in a drying frying pan until golden-brown all over.
Remove the cashew nuts from the pan and chop roughly.
Add the sugar to the pan used to cook the cashew nuts and cook for 2-3 minutes, or until the sugar has melted and becomes caramel. Add the chopped nuts and swirl the pan until well combined.
Pour the mixture onto the baking tray and set until cool, then break the brittle into small pieces.
Blend half of the brittle in a food processor until smooth and sprinkle onto a plate.
For the cheesecake, blend the ricotta, yoghurt, 110g/4oz of the sugar and the vanilla seeds in a bowl and whisk until well combined. Fold in the double cream and half of the reserved pieces of cashew brittle.
Spoon the mixture into four 6cm/2½in chefs’ rings then dip one end into the blended cashew brittle.
Heat a frying pan until hot, add the butter and bananas and fry for 1-2 minutes, then add the remaining sugar and cook for a further 2-3 minutes.
To serve, place the cheesecake, cashew-side down, into the centre of each of four serving plates. Use a blowtorch or a warm towel to loosen the chef’s rings then carefully lift them off.
Top the cheesecake with some shards of the cashew brittle and spoon the bananas alongside.