Simmer the water, glucose and sugar until the sugar has dissolved. Add the lemon zest and juice and frozen berries. Blend to a smooth puree then pass through a sieve. Place in a plastic tray and freeze. After an hour fluff up with a fork and do this hourly for 4 hours when you should have grainy crystals.

Whisk together topping ingredients.

Spoon granita into 4 bowls or glasses and then top with a spoon of the yoghurt.