In a saucepan, bring 1 cup sugar and 2 cups water to a boil. Let cool slightly then measure out 2 cups. Combine the 2 cups with the lemon juice and chill.
Meanwhile in a saucepan, place the blackberries with 1 tablespoon of water and 3 tablespoons of sugar. Bring to a boil then turn the heat down to a simmer, stirring often to reduce to a thick puree. Strain, if desired and chill the puree.
Spin the chilled sorbet mixture in your ice cream maker then place in a frozen bowl. Fold in the chilled blackberry puree lightly to swirl it. Freeze until ready to enjoy.