In a mixing bowl, combine crushed chocolate sandwich cookies with melted unsalted butter, stirring until fully moistened. Press firmly into the bottom of silicone molds.

In a saucepan over medium heat, combine blackberries, granulated sugar, water, and fresh lemon juice. Cook for 5-7 minutes until berries are soft. Strain through a fine mesh sieve to remove seeds.

Sprinkle unflavored gelatin over cold water in a small bowl. Let sit for 5 minutes. Heat blackberry puree, whisk in the dissolved gelatin.

In a heatproof bowl, combine white chocolate chips and heavy cream over a double boiler. Stir until melted and smooth. Cool to room temperature.

Mix cooled blackberry puree with melted white chocolate and vanilla extract. Gently fold in whipped heavy cream.

Carefully pour mousse over the cooled crust in each mold. Tap molds on the counter to release air bubbles.

Cover molds with plastic wrap and refrigerate for 4-6 hours, or overnight until firm.

Demold the Mini Blackberry Mousse Cakes by inverting the molds onto a plate. Garnish with fresh blackberries and edible flowers.