Preheat oven 170°C. Grease a 20cm deep round cake pan; line base and side with baking paper, extending the paper 4cm above the top.
Beat butter, caster sugar and rind in a large bowl with an electric mixer until pale and fluffy. Beat in eggs, one at a time, until combined. Fold in sifted flour, then almond meal and sour cream. Spoon half the mixture into pan; top with ¼ cup of the blackberries, pressing lightly into the mixture. Top with remaining cake mixture and another ¼ cup of the blackberries; smooth surface. Tap pan on a work surface to settle mixture.
Bake cake for 1 hour 10 minutes or until a skewer inserted in the centre comes out clean. Stand cake in pan for 10 minutes.
Meanwhile, stir juice, the water and extra caster sugar in a small saucepan over medium heat until sugar dissolves. Bring to the boil. Reduce heat; simmer for 2 minutes. Cool for 5 minutes.
Pour hot syrup over cake in pan. Stand for 20 minutes before turning, top-side up, onto a wire rack to cool completely.
Combine remaining berries and any juices with icing sugar in a small bowl; set aside to completely thaw. Crush lightly with a fork.
Beat cream in a large bowl with an electric mixer until soft peaks form.
Spoon cream on top of cake, drizzle with remaining berry mixture, swirling lightly through cream.