Preheat the grill to a high temperature. Fill 4 x 150 ml (1/4 pint) ramekin dishes with blackberries. Cover blackberries with a layer of the Greek yoghurt and smooth over with top with a flat knife.
Sprinkle an even layer of caster sugar over each one, completely covering the yoghurt, and lay on a sturdy baking sheet. Place under the hot grill for 30 seconds to 1 minute or until the sugar has just melted and caramelised – alternatively you can use a mini blowtorch for this. Allow the sugar to cool and set for one minute or so before serving.