Grate the zest of 1 lemon and place into a bowl, if using. Peel and chop all the lemons up into quarters and grate them into a saucepan.
Pour hot water over the lemons and add lemon zest, if using. Add the sugar and put the pan on the hob and leave to boil, as you are waiting get out a bowl.
When the mixture is boiling in the pan take it off the hob and pour into the bowl. Put the dish with the mixture in the fridge to cool down so the dish doesn't crack and then freeze for about 4 hours, until it is frozen the whole way through.
Serve and enjoy!
A good alternative for ice-cream, if you are allergic to dairy products.