Place the sugar and raspberries in a food processor and process until just combined. Place the apple and half of the sugar mixture in a bowl and gently toss to coat. To serve, place a slice of each apple on a plate. Top with one scoop of sorbet, another slice of each apple, and finish with another scoop of sorbet. Repeat with the remaining ingredients. Sprinkle with the remaining raspberry-sugar to serve. Serves 4.