Quarter the pineapple and cut out the stalk. Cut the flesh from the skin. Wash the nectarines, drain, cut in half and remove the stone. Cut the flesh into very small pieces.
Mix 4 tablespoons of sugar and gelling powder. Mix with the fruit and bring to a boil while stirring. Add the rest of the sugar and boil for 1 minute until bubbly. Wash lemon balm, dab dry, remove leaves and cut into strips.
Stir lemon and lemon balm into the boiling jam. Pour hot into prepared glasses and close immediately. Results in about 8 glasses.