Prepare the Berries: Wash the lilly pilly berries thoroughly, removing any stems and leaves. Place them in a large saucepan with 2 cups of water.
Cook the Berries: Bring the mixture to a boil, then reduce to a simmer. Cook for 15-20 minutes until the berries burst and soften.
Extract the Juice: Strain the cooked mixture through a fine sieve or cheesecloth to remove seeds and skins. Press gently to extract as much juice as possible.
Make the Jelly: Return the strained juice to the saucepan. Add the lemon zest, lemon juice, and sugar. Stir to dissolve the sugar, and bring the mixture to a boil. After boiling, add the pectin and stir well.
Test the Jelly: Let the mixture simmer for 10-15 minutes. To check if it’s set, place a spoonful on a cold plate—run your finger through it. If it wrinkles and doesn’t run, it’s ready.
Jar the Jelly: Pour the jelly into sterilized jars, seal, and let them cool. The jelly will continue to set as it cools.