Count one kilo of sugar for each kilo of handpicked blackberries, and the juice of two lemons. Bring the berries to the boil and allow to simmer until juicy. Add the sugar and the lemon juice and allow a rolling, bubbling boil for about 3 minutes. Test for consistency. (A drop on a cold saucer should not be runny, when cooled.) Allow an extra minute if not correct. Pour into warm jam jars that have been washed in hot soda water. Seal immediately. Thus enjoy the taste of summer during the winter months.