Blend the Oreo cookies for the layer in a blender. To them, add the pre-chopped walnuts, butter at room temperature.
Put the cake ring in a suitable plate for a cake. Pour the mixture in it, distribute it and press lightly with a spoon. Put the cake layer in the fridge for 30 min. to harden.
In a bowl, mix together the mascarpone, sour cream, cream cheese and sugar, while stirring very well. Flavor with the vanilla. Pour the gelatin in about 2/5 cup (100 ml) of cold water so that it soaks and swells.
Then melt it in a water bath and pour it into the cream, stirring very well with a spatula.
Pour half of the cream over the cooled layer. Crumble the 12 Oreo cookies coarsely and spread them all over the cream.
Pour the rest of the cream on top and smooth it out. Return to the fridge to sit for a few hours; overnight is best.
Decorate the cake the next day.
For the decoration: Crumble the dark chocolate in a bowl and leave it in a water bath with the milk and butter to melt. Remove the cake ring.
Pour on 1 tbsp of the melted chocolate over the cake. Arrange the frozen fruits over the chocolaty part. If you have fresh fruits on hand, even better.
Sprinkle the fruits with the dissolved gelatin. The powdered gelatin comes in a packet, just follow the directions for its preparation. In my case, I poured a cup of cold water over the powdery contents.
Dissolve it well and boil on the stove, along with 3 tbsp of sugar, very briefly. Leave it to cool for 1 min. and pour the gel over the fruits immediately.