Begin by crushing the chocolate sandwich cookies in a food processor until they resemble fine crumbs. Melt the unsalted butter and mix it with the cookie crumbs until fully combined. Firmly press the mixture into the base of silicone molds or ring molds, ensuring an even layer. Place the molds in the freezer for about 15 minutes to set while you prepare the mousse.

In a medium saucepan, combine fresh or frozen blackberries, sugar, and water. Cook over medium heat for about 5–7 minutes, stirring occasionally, until the blackberries soften. Use a blender to puree the mixture, then strain it through a fine sieve to remove the seeds, returning the smooth puree to the pan. Bloom the gelatin in lemon juice, then stir it into the warm blackberry puree until fully dissolved.

Allow the blackberry puree to cool slightly before proceeding. In a mixing bowl, whip the heavy cream until soft peaks form. Gently fold the whipped cream into the blackberry mixture until well combined and smooth, creating a light and airy mousse. Take care not to deflate the cream as you blend.

Pour the blackberry mousse evenly over the chilled chocolate crusts in the molds, smoothing the tops with a spatula. Refrigerate the mini cakes for at least 4 hours or until the mousse is fully set and firm to the touch.

In a small saucepan, gently heat the heavy cream just until it begins to simmer. Pour the hot cream over the white chocolate chips in a mixing bowl. Let sit for a minute, then stir until the chocolate is fully melted and the glaze is smooth. Allow the glaze to cool slightly until it reaches a lukewarm temperature.

Once the mousse has set, carefully remove the mini cakes from the molds. Pour the white chocolate glaze over each set mousse cake, allowing it to cascade down the sides for a beautiful finish. Finally, garnish each cake with fresh blackberries and the edible flowers for an elegant presentation.