Add the cassis to the 1 3/4 cups blackberries and mash lightly with a fork.
Whip the cream in a large bowl until thick but still soft. Roughly crumble in 1 of the meringues nests - you will need chunks for texture as well as fine dust.
Fold in the fruit mixture and arrange on a serving plate in a mound, then crumble over the remaining meringue. Decorate with the remaining 1/4 cup blackberries.