Put water, 1/2 cup of granulated sugar and vanilla sugar in a saucepan and heat. When the sugar is dissolved, set it aside and gradually add the instant dry milk, stirring constantly. Let it cool for a while. Then add butter to the mixture and beat everything with a mixer into a smooth cream.
Then separate approx. 8 oz of this mass and add it to the crushed cookies, which you have mixed in a bowl with ground walnuts and milk.
Layer the mass on the bottom of an approx. 8 in' diameter mold, which you have lined with baking paper. Put it in the refrigerator.
Now, let's prepare the fillings. Melt each type of chocolate separately in a water bath. Divide the remaining cream in half, add melted white chocolate to one part and melted dark chocolate to the other part. Beat with a mixer.
Layer the dark cream on the cake base, put it in the fridge for half an hour and then layer the white chocolate cream. Whip the whipping cream with stabilizer and spread it on top. Decorate according to your imagination. Enjoy!