1 Rinse the blackberries and drain well.
2 Rinse elderberries, drain well and pluck from the stems.
3 Put all the berries in a pot and add 150 ml (approximately 1/2 cup) water.
4 Cover pot and slowly bring mixture to a boil, then reduce heat and simmer for about 30 minutes, stirring occasionally.
5 Line a fine sieve with a kitchen towel and set over another pot. Pour the berry mixture into the sieve and let drain for 5-6 hours.
6 Measure out 1.2 liters (approximately 5 cups) of the berry juice. Combine juice and jelling sugar in pot and bring to a boil, stirring constantly.
7 Continue to boil juice mixture for 4-6 minutes, skimming off any foam from the surface as needed. Squeeze juice from lemon and stir 2 tablespoons juice into jelly. Cook for another 30 seconds.
8 Ladle into jars, cover with lids and refrigerate for up to 2 weeks.
Tip: To store longer, process jars according to manufacturer's instructions (or visit http://nchfp.uga.edu/).