Allow 20 minutes preparation time and 15 minutes churning in the ice cream maker, if you have one. If you don’t, follow the instruction below, but it will take longer. Defrost the raspberries and blitz them to a purée. Sieve the purée and add the lemon juice and the sugar to it. Mix well until the sugar has dissolved then churn the sweetened purée in an ice-cream maker until it is smooth and frozen.

If you don’t have a machine, pour the purée into a shallow plastic dish and place it in the freezer. Stir it with a fork or whisk after about 45 minutes when it has started to freeze well, then again every 30 minutes or so for the next couple of hours, until it’s properly frozen, to break up ice crystals.