Place berries in a large bowl. Add 1/4 cup sugar and 2 tablespoons cassis, 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 sugar, and 2 tablespoons cassis 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. Sprinkle with chopped hazelnuts and garnish with mint.