Mix chocolate cookie crumbs with melted butter. Press into silicone dessert molds and chill for 20 minutes.
Sprinkle gelatin over cold water, let bloom for 5 minutes, then microwave for 10 seconds until liquid. Divide into three equal portions.
Melt dark, milk, and white chocolates in separate bowls. Stir one portion of the liquid gelatin into each bowl. Let cool to room temperature.
Whip cold heavy cream to soft peaks.
Divide whipped cream into thirds. Fold one third into the cooled dark chocolate. Layer over crusts and freeze for 10 minutes.
Fold the second third of cream into the milk chocolate. Layer over dark chocolate and freeze for 10 minutes.
Fold remaining cream into white chocolate. Add the final layer and smooth tops.
Chill cakes for at least 4 hours before unmolding and dusting with cocoa powder to serve.
