Wash, drain and puree the blackberries. Stone, peel and cut the washed peaches into small pieces or puree them.
Mix the fruits with sugar and lemon juice and bring to the boil, stirring constantly. Make a gelling test and then pour it into hot-washed glasses.
A little tip: if you don`t like the stones from the blackberries in the jam, you can rub the pureed fruit through a sieve! So you only have the fruit pulp left.