500g Raspberries, plus more to serve (optional)
1 Lemon, juiced
1. Put the Zùsto and 270ml water in a saucepan over a low heat and stir until the Zùsto has dissolved. Raise the heat and simmer for 5 mins, or until the liquid has become a syrup. Set aside to cool.
2. Put the raspberries and lemon juice in a food processor and blitz until smooth. Strain through a fine sieve into a bowl and discard the seeds. Combine with the Zùsto syrup, then pour into freezer-proof container.
3. Freeze for 1 hr 30 mins, then whisk with a balloon whisk or a fork to break up any ice crystals that have formed and return to the freezer.
4. Keep mixing the sorbet once an hour for 4 hrs to break up the ice crystals. Stop mixing when firm but scoopable. Will keep in the freezer for up to a month. Serve with extra raspberries, if you like.