Add the water, keto-friendly sweetener and lemon peel to a pan. When removing the peel from the lemon ensure you don’t get any white pith or this can make the syrup bitter. Heat on a low heat until the sweetener dissolves and thickens slightly to a syrup, about 7 minutes. Leave to cool. Discard the lemon peel.
Juice the lemons. Add the lemon juice to the cooled syrup and stir.
Pour the lemon mix into ice cube trays or a non-stick loaf tin, cover with cling film and freeze for 3 hours or until solid. Option to leave overnight. (I did.)
When frozen, release the ice cubes or run the sides of the loaf tin under hot water to loosen the frozen sorbet. Tip onto a chopping board and chop into chunks. If you’ve left it overnight you’ll need to give it a good smash.
Place the chunks in a high speed food processor and blitz until smooth. The smaller you cut the cubes the easier it is. You may need to scrape and blitz several times until it all combines, depending on how long you left it in the freezer.
Once combined, pour the sorbet back into your loaf tin and freeze for about 1.5 - 2 hours until just scoop-able. If you leave it to set to much by mistake, simply repeat the step of chopping into chunks and blitzing. You can repeat this step if you don’t eat all your sorbet in one go and leave in the freezer for several weeks.
Serve scoops of sorbet decorated with a few curls of lemon zest.
Option to make the sorbet in an ice cream maker. To do this, simply make the syrup as per the instructions above. Chill in the freezer for about 30 minutes. Pour into an ice cream maker and churn as per manufacturers instructions. When nice and slushy transfer to a non stick loaf pan, cover with cling film and freeze for about 2 hrs until scoop-able.