The day before, place the frozen strawberries in a sieve or colander over a bowl so that the bowl collects all the juices as the strawberries defrost.

Sprinkle the gelatin over the strawberry juices that have collected in the bowl and leave to soak for 5 minutes.

Put the lemon juice and sweetener in a small pan and warm them over a low heat just until the sweetener is dissolved and the liquid is clear. Do not overheat.

Turn off the heat, add the soaked gelatin and juice to the pan and stir well until the gelatin has dissolved.

Place the strawberries in the bowl that collected the juices and mash well with a potato masher, or you can use a stick blender in short bursts so some of the strawberries remain chunky.

Pour the syrup from the pan into the mashed strawberries and mix well.

Pour into a jar or similar container and put in the fridge to set.