Rinse raspberries and blackberries and pat dry. Soften gelatin in cold water. Combine 200 grams (approximately 7 ounces) raspberries and 50 grams (approximately 2 ounces) blackberries with sugar, puree and strain through a sieve.
Squeeze gelatin, heat in a small saucepan with 4 tablespoons raspberry juice and dissolve. Stir blackberry liqueur into half of the fruit puree. Beat cream until stiff and fold in. Mix the other half of the fruit puree with 2 tablespoons raspberry juice.
Fill serving ramekins with fruit mousse and place in the refrigerator for at least 4 hours. Place mousse on small plates, drizzle each with fruit puree and serve garnished with mint leaves and remaining raspberries and blackberries.