Cut the apples up into chunks, keeping the peel and the core. Combine the water, apples and lemons sliced in half in a pot and bring to a boil. Boil until the apples turn to mush – approx. 40 minutes. Pour the liquid through a fine-meshed cloth.
When you’ve retrieved all the liquid, bring it to a boil with the sugar. Boil for 10 minutes. Skim off any impurities and foam as they will make the jelly cloudy. Pour into jars.