Place berries in a large bowl, add 1/4 cup of sugar and 2 tablespoons of cassis, if using, stir well and let sit at room temperature for 30 minutes. Remove half of the berries and mash with fork until pureed. Strain the mixture into a bowl.
Whip heavy cream, 3 tablespoons of sugar and 2 tablespoons of the cassis, if using, in a large bowl until stiff peaks form. Fold in the white chocolate and strained puree and chill for 1 hour. Layer goblets with berry cream mixture and whole macerated berries. Garnish with mint.