Place a pan over a low heat, and add the sugar and 100ml water. Stir until the sugar has dissolved, then pour into a jug.
Squeeze in the clementine and lemon juice into the jug, then add the pomegranate juice and chill in the fridge. When cold, pour into a shallow container and place in the freezer.
When ice crystals have formed around the edges, whisk it and return to the freezer. Repeat 4 times until you have a smooth sorbet. Or, freeze the mixture until solid, then blitz in a food processor and return to the freezer until ready to serve.