Crush chocolate sandwich cookies in a food processor until fine crumbs. Mix with melted unsalted butter and press into silicone molds. Freeze for 15 minutes.

Cook blackberries, sugar, and water in a saucepan over medium heat for 5-7 minutes, stirring occasionally until softened. Blend until smooth and strain through a sieve.

Mix gelatin with lemon juice in a bowl and let bloom for 5 minutes. Warm a portion of blackberry purée to dissolve gelatin, then combine and cool to room temperature.

Whip heavy cream in a mixing bowl until soft peaks form. Fold in cooled blackberry purée and vanilla extract gently.

Pour blackberry mousse over the chilled crusts in molds, spreading evenly. Cover with plastic wrap and refrigerate for at least 4 hours to set.

Gently heat heavy cream until warm, then pour over white chocolate chips. Stir until melted and smooth. Let cool slightly before applying.

Remove mousse cakes from molds and place on a platter. Drizzle cooled glaze over tops and garnish with fresh blackberries and edible flowers.