Peel and cut 2 bananas in half lengthways. Put them cut-side up on a roasting tray and sprinkle the caster sugar over. Use a kitchen blowtorch or put them under a hot grill until the sugar has caramelised then leave to cool for a few minutes.
Peel and mash the remaining bananas with a fork then mix with the lemon juice and honey.
Whisk the crème fraîche and yoghurt together until smooth and thickened slightly. Fold in the crushed banana mixture and add half the crushed amaretti.
Put the caramelised bananas into 4 serving glasses (cut them in half if they’re too long) and spoon the banana mixture over. Sprinkle with the remaining amaretti and drizzle with a little more honey to serve.